DE102022005060B4 - Sensor element and method for producing a sensor element - Google Patents

Abstract

Sensor element (100) for measuring a temperature comprising
- at least one carrier (2) having a top side (11) and a bottom side (12), wherein an electrically insulating layer (3) is formed on the top side (11) of the carrier (12), wherein the electrically insulating layer (3) completely covers the top side (11) of the carrier (2),
- at least one functional layer (7) comprising a material with a temperature-dependent electrical resistance, wherein the functional layer (7) is arranged on the electrically insulating layer (3),
- at least two electrodes (4a, 4b) which are formed on the carrier (2) at a distance from one another, wherein the respective electrode (4a, 4b) has a plurality of electrode fingers (5), wherein the electrode fingers (5) of the two electrodes (4a, 4b) are arranged alternately with one another and wherein at least one of the electrode fingers (5) has a comb-shaped region, wherein the comb-shaped region has a plurality of teeth (20) which point in the direction of the subsequent electrode finger (5),
and wherein at least one of the electrode fingers (5) has a different shape than the other electrode fingers and wherein the at least one electrode finger (5) is trapezoidal or triangular,
- at least two contact pads (10a, 10b) for electrically contacting the sensor element (100), wherein each contact pad (10a, 10b) is arranged directly on a partial area of one of the electrodes (4a, 4b),
wherein the sensor element (100) has a maximum edge length of
< 500 µm and a thickness < 50 µm, wherein the sensor element (100) is designed as a discrete component to be integrated directly into an electrical system, wherein the sensor element (100) is designed for direct integration into a MEMS structure and/or into a SESUB structure, wherein the sensor element (100) has a narrow resistance tolerance.

Description

The present invention relates to a sensor element, in particular a temperature sensor. The present invention further relates to a method for producing at least one sensor element, preferably a temperature sensor.

To integrate passive components such as sensors, capacitors, protective devices, or heaters into electrical systems, the dimensions must be adapted to modern packaging designs, which are in the micrometer and even nanometer range. To achieve this level of miniaturization, the components are deposited as thin films on carrier structures with electrical connections and described as discrete components. These novel components can be integrated into MEMS (Micro Electro Mechanical System) or SESUB (Semiconductor Embedded in Substrate) structures, among others.

The increasing demands on temperature measurement accuracy require tight tolerances in the resistance variation of such sensor elements. However, with ever-smaller structures, manufacturing tolerances have an increasingly greater influence, causing the resulting resistance variation to exceed the required tolerances. Resistance variation can only be reduced to a limited extent through process control.

Current technology primarily uses ceramic thermistor elements (NTCs), silicon temperature sensors (KTYs), platinum temperature sensors (PRTDs), or thermocouples (TCs) to measure temperatures for monitoring and control in a wide variety of applications. NTC thermistors are the most widely used due to their low manufacturing costs. A further advantage over thermocouples and metallic resistance elements, such as Pt elements, is their pronounced negative resistance-temperature characteristic.

For use in power modules, SMD (surface-mounted device) NTC temperature sensors are primarily used. For low-power control modules, NTC chips are also used. These are mounted on the underside using Ag sintering paste, soldering, or adhesive, and the top side is contacted via a bonding wire.

To electrically connect the NTC chips, metallic electrodes must be applied. Current technology involves applying thick-film electrodes, primarily made of silver or gold pastes, using a screen-printing process followed by firing.

The integration of electronic components into structures such as MEMS or SESUB requires very small elements, which must also be integrated using suitable contacting techniques. Conventional assembly technologies for SMD packages or NTC chips cannot be used for this purpose.

The document US 2003/0 062 984 A1 describes a thin-film thermistor with a cut section of a metallic pattern for resistance adjustment.

The document US 2016/0 093 423 A1 describes a phase-locked loop for estimating the phase angle of a three-phase reference signal.

The document JP 2013 - 197 367 A describes a thin-film thermistor used in an infrared sensor and used for temperature detection, human detection sensors, and the like.

The document WO 2013 / 147 290 A1 describes a thermistor material used for a temperature sensor or similar that has a high B constant for high accuracy and high sensitivity.

The document DE 10 2014 104 219 A1 describes a ceramic carrier on which a thin-film structure made of platinum or a platinum alloy is arranged, wherein the carrier and/or the thin-film structure are adapted to reduce mechanical stresses due to different thermal expansion coefficients.

The German patent application DE 10 2020 122 923 A1 , the content of which is incorporated by reference into this application, describes a sensor element for temperature measurement using a thin-film NTC thermistor.

Until now, thin-film NTC temperature sensors could not be manufactured with tolerances as tight as classic designs (SMD NTC and NTC chips).

The object of the present invention is to describe a sensor element and a method for producing a sensor element which solve the above problems.

This object is achieved by a sensor element and a method for producing a sensor element according to the independent claims.

According to one aspect, a sensor element is described. The sensor element 1 is suitable for measuring a temperature. The sensor element is a temperature sensor. Preferably, the sensor element is a thin-film NTC temperature sensor.

The sensor element has at least one carrier. Preferably, the sensor element has exactly one carrier. The carrier has a carrier material, preferably silicon, silicon carbide, GaN, or glass (silica or borosilicate glass). Alternatively, the carrier material can also comprise Si ₃ N ₄ , AlN, or Al ₂ O ₃ .

The carrier has a top side and a bottom side. The top side is electrically insulating. Preferably, an insulating layer, for example Al ₂ O ₃ , AlN, SiO ₂ or Si ₃ N ₄ or combinations of layers of these materials, is formed on the top side of the carrier. The insulating layer is formed directly on the top side of the carrier and can be composed of one or more layers.

The sensor element further comprises at least one functional layer. The functional layer is arranged on the carrier. In particular, the functional layer is arranged on the electrically insulating upper side of the carrier.

The carrier mechanically stabilizes the functional layer. The functional layer can be formed directly on the carrier. Alternatively, additional components of the sensor element, such as electrodes, can be formed between the carrier and the functional layer.

The thickness of the functional layer is between 50 nm and 1 µm, preferably between 100 nm and 500 nm, particularly preferably between 250 nm and 400 nm. The functional layer comprises a material (functional material) that has a specific electrical characteristic. The functional layer comprises a material with a temperature-dependent electrical resistance. The functional layer preferably comprises an NTC ceramic. The functional layer is preferably a thin film with NTC characteristics.

The NTC ceramic is preferably based on an oxide material with a perovskite or spinel structure. Alternatively, the functional layer can be based on a carbide or nitride material. Thin films of vanadium oxide or SiC are another alternative.

The sensor element further comprises at least two electrodes. The electrodes are preferably formed as thin-film electrodes. The electrodes are formed on the carrier at a distance from one another. Preferably, the electrodes do not extend to an edge region of the carrier. In particular, the electrodes are preferably formed in a central or inner region on the carrier. Each electrode has a plurality of electrode fingers. The electrode fingers of the two electrodes are arranged alternately with one another. The electrodes thus form an interdigital structure.

The sensor element further comprises at least two contact pads for electrically contacting the sensor element. Preferably, the sensor element comprises exactly two contact pads. The contact pads are directly electrically and mechanically connected to the electrodes. Each contact pad is arranged directly on a portion of one of the electrodes.

The sensor element is very compact. In particular, the sensor element is designed to be embedded as a discrete component directly into an electrical or electronic system. For example, the sensor element has a maximum edge length of 1000 µm, preferably <800 µm, particularly preferably <500 µm. The thickness of the sensor element is <100 µm, preferably <80 µm, particularly preferably <50 µm. The component is preferably designed for direct integration into a MEMS structure and/or a SESUB structure.

The sensor element also features a narrow resistance tolerance. This means that the sensor element has a very small deviation range from a nominal resistance (nominal resistance value).

The at least one functional layer and/or at least one of the at least two electrodes are structured to adjust the resistance value. The at least one functional layer and/or at least one of the at least two electrodes are trimmable to adjust the resistance value. In particular, at least a partial region of the at least one functional layer and/or at least a partial region of at least one of the two electrodes is severed to adjust the resistance.

If the resistance of the component to be trimmed already corresponds to the target value, the structured / trimmable areas are not severed.

By achieving a tight resistance tolerance, the sensor element exhibits very high temperature measurement accuracy. Preferably, the sensor element has a resistance tolerance comparable to the tight resistance tolerance of conventional designs such as SMD NTCs or NTC chips.

According to one embodiment, the functional layer only partially covers the carrier or the insulating layer on top of the carrier. Furthermore, the functional layer only partially covers the electrode fingers of the two electrodes.

The geometry/arrangement of the functional layer is initially selected such that the functional layer covers the carrier/insulating layer only in the area of the finger structure of the electrodes. Preferably, the functional layer is formed only in a central region of the carrier. In particular, the functional layer does not extend to an edge region of the carrier. Furthermore, the structure of the functional layer is selected such that a specific resistance (setpoint) of the sensor element can be set. This makes the sensor element particularly flexible and particularly precise.

According to one embodiment, the functional layer comprises a plurality of strips. In other words, the functional layer consists of discrete individual elements. The strips are arranged at a distance from one another. The strips are arranged parallel to one another.

The sensor element's design is based on the principle of a parallel connection of individual resistors. The strips are perpendicular to the electrode fingers and are contacted via them. This results in several individual resistors connected in parallel between the electrode fingers.

The strip width can be the same for all strips of the functional layer. Alternatively, the strip width can also vary. For example, very narrow, medium, and wide strips can be combined. This allows for greater variance in the resistance setting. In a parallel circuit, where the individual resistors are added as reciprocals, this means that trimming larger resistors results in a small change in resistance across the entire sensor element. This allows for easy fine-tuning of the resistance setpoint.

Trimming can be performed in two ways. Either the functional layer or the electrode fingers can be severed. In particular, to adjust the resistance value of the sensor element, at least one strip of the functional layer and/or at least one electrode finger is severed, preferably by means of a laser (laser trimming).

According to one embodiment, the functional layer or at least a portion of the functional layer is stepped, trapezoidal, or triangular. The functional layer therefore does not have any discrete individual elements, but is formed as a single piece. However, the functional layer only partially covers the electrodes, in particular the electrode fingers.

The specific structure of the functional layer and the only partial overlap of the electrode fingers result in different individual resistances, which are connected in parallel between the electrode fingers. This allows for easy trimming to a desired target resistance. To adjust the resistance value, at least one electrode finger is severed, particularly using a laser (laser trimming). Another possible method for adjusting the resistance value is to cut the functional layer along an electrode finger (i.e., between the electrode fingers) using a laser.

According to one embodiment, at least one electrode finger is structured. In particular, at least one of the electrode fingers has a different shape than the other electrode fingers. Preferably, at least one of the electrode fingers is trapezoidal or triangular. In comparison, the other electrode fingers have a square shape. This results in an even finer resistance adjustment option due to a wider spread of the trimmable individual resistors between two adjacent electrode fingers.

According to one embodiment, the electrode fingers of at least one of the at least two electrodes are configured to be of different lengths. In other words, at least one, preferably exactly one, of the two electrodes has electrode fingers of different lengths.

This results in different individual resistances of the electrode fingers, which are connected in parallel between the electrode fingers, thus allowing trimming to the desired target resistance. To adjust the resistance value, at least one of the electrode fingers of different lengths is severed, particularly with the aid of a laser.

According to one embodiment, the distance between adjacent electrode fingers varies. This provides additional areas with varying distances for trimming, resulting in even finer gradations in the resistance setting. To adjust the resistance value, at least one of the electrode fingers is severed, in particular with the aid of a laser.

According to one embodiment, at least one of the electrode fingers has a comb-shaped region. The comb-shaped region has a plurality of teeth. The teeth point toward the subsequent electrode finger. The comb-shaped region is preferably formed on one of the outer electrode fingers.

The teeth of the comb-shaped area can be of different lengths and/or widths.

This allows for greater variance in resistance adjustment. In particular, different individual resistances result, allowing trimming to the desired target resistance. To adjust the resistance value of the sensor element, at least one of the teeth is cut.

According to one embodiment, the electrodes are formed directly on a top side of the functional layer. In other words, the functional layer is formed between the electrodes and the carrier. This design allows trimming of the electrode after application and testing of the sensor element. Furthermore, in this design, the electrode does not have to withstand the conditions of the sintering process of the functional layer. Alternatively, the electrodes can also be arranged directly on a bottom side of the functional layer.

According to one embodiment, the sensor element has a protective layer. The protective layer can be made of oxides, nitrides, ceramics, glasses, or plastic. The protective layer completely covers a top surface of the sensor element, with the exception of the contact pads. For this purpose, the protective layer has recesses at the location of the contact pads. The protective layer has a thickness of <10 µm, preferably <5 µm, ideally <1 µm. The protective layer improves the long-term stability of the sensor element.

According to a further aspect, a method for producing at least one sensor element, in particular a plurality of sensor elements, is described. It should be noted that the method preferably involves producing many sensor elements in parallel and subsequently separating them from one another. For the sake of simplicity, reference will be made below primarily to one sensor element.

1. A) Bereitstellung eines Trägermaterials zur Ausbildung eines Trägers. Vorzugsweise weist das Trägermaterial Si, SiC, GaN oder Glas auf. Alternativ dazu kann das Trägermaterial Si₃N₄, AlN oder Al₂O₃ aufweisen. Der Träger weist eine Oberseite und eine Unterseite auf. Auf der Oberseite des Trägermaterials kann ferner eine elektrisch isolierende Schicht, vorzugsweise SiO₂, ausgebildet werden.
2. B) Ausbilden bzw. Abscheiden von wenigstens zwei Elektroden auf dem Träger. Das Abscheiden erfolgt durch einen PVD („physical vapour deposition“) Prozess, einen CVD („chemical vapour deposition“) Prozess oder galvanisch. Alternativ dazu kann das Abscheiden auch durch ein ALD (Atomic Layer Deposition) Verfahren erfolgen.

Preferably, the method produces the sensor element described above. All properties disclosed with respect to the sensor element or the method are also disclosed correspondingly with respect to the respective other aspect, and vice versa, even if the respective property is not explicitly mentioned in the context of the respective aspect. The method comprises the following steps:

1. A) Providing a carrier material for forming a carrier. The carrier material preferably comprises Si, SiC, GaN, or glass. Alternatively, the carrier material may comprise Si ₃ N ₄ , AlN, or Al ₂ O ₃ . The carrier has a top side and a bottom side. An electrically insulating layer, preferably SiO ₂ , may also be formed on the top side of the carrier material.
2. B) Forming or depositing at least two electrodes on the substrate. The deposition is carried out using a PVD (physical vapor deposition) process, a CVD (chemical vapor deposition) process, or electroplating. Alternatively, the deposition can also be carried out using an ALD (atomic layer deposition) process.

The electrodes are formed spaced apart from one another. In particular, the electrodes are spatially and electrically insulated from one another. The electrodes have electrode fingers. The electrodes interlock in the form of interdigital structures. The electrodes are preferably formed directly on the upper side of the carrier or on the insulating layer. Alternatively, the electrodes can also be formed on the upper side of the functional layer. The electrodes are formed such that they are spaced apart from an edge region of the carrier.

The electrodes can be structured to adjust the resistance of the sensor element (see step E).

C) Applying, preferably sputtering, a functional material to a portion of the electrodes to form a functional layer. The functional material preferably comprises an NTC ceramic based on an oxide material in the perovskite or spinel structure type. Alternatively, the functional material can also be based on a carbide or nitride material. Alternatively, the functional material can be a comprise or represent a thin film of vanadium oxide or SiC.

The functional layer is formed as a thin film. The functional layer only partially covers the substrate or the electrodes. Specifically, the functional layer is formed so that it is spaced from the edge region of the substrate and positioned in the area of the finger structures (interdigital structures) of the electrode. The functional layer is deposited as a full-surface thin film and is only structured in a subsequent process step, e.g., using wet-chemical etching or dry etching. After deposition, the NTC layer is not yet crystallized.

The functional layer can be structured to adjust the resistance of the sensor element (see step E).

D) Temperature treatment of the functional layer. This serves to develop the NTC properties of the functional material and is carried out at temperatures up to 1000°C.

The functional layer is then measured. This determines the initial tolerance range of the resistance value. At this stage of the process, this tolerance range is, for example, the nominal resistance value ± 5%.

E) Adjusting the resistance value of the sensor element. This is done by trimming at least one of the electrodes and/or the functional layer using a laser. The resistance value is adjusted to a predetermined nominal value (target value). By precisely adjusting the resistance value, the finished sensor element has a very tight resistance tolerance. The resistance tolerance of the nominal value of the finished sensor element is a maximum of ± 5%, preferably a maximum of ± 1%, particularly preferably a maximum of ± 0.5%.

The functional layer and/or at least one of the electrodes, for example, at least one electrode finger, are structured to adjust the resistance. In other words, the functional layer and/or at least a portion of the electrodes have a structured region. The initial resistance of the functional layer is selected such that it lies within a tolerance window at low resistance values.

The final resistance value is adjusted by trimming the structured region. Specifically, at least one of the electrode fingers and/or at least a portion of the functional layer is severed using a laser. In other words, material is removed from at least one electrode finger and/or at least a portion of the functional layer, changing the resistance of the respective component and thus the overall resistance of the sensor element. The resistance of the sensor element is increased to the target value by trimming the structured regions.

However, if the resistance of the sensor element already corresponds to the target value, no additional adjustment of the resistance value is required.

• F) Aufbringen einer Schutzschicht auf die Oberseite des Sensorelements. Die Schutzschicht bedeckt die Oberseite bis auf zwei Teilbereiche vollständig. Die Teilbereiche sind über einen flächigen Endbereichen der Elektroden angeordnet, auf die im nachfolgenden Prozessschritt die Kontaktpads aufgebracht werden können. Die Schutzschicht wird zur Strukturierung entweder
  1. (a) vollflächig aufgebracht und die freien Teilbereiche durch einen Folgeprozess wie nasschemisches Ätzen oder Trockenätzen oder Laserstrukturierung erzeugt oder
  2. (b) durch Verwendung einer Maske beim Abscheidungsprozess direkt strukturiert aufgebracht.
• G) Ausbilden von Kontaktpads in den von der Schutzschicht freien Teilbereichen zur elektrischen Kontaktierung des Sensorelements. Jeweils ein Kontaktpad wird dabei unmittelbar auf einem flächigen Endbereich einer der Elektroden ausgebildet. Die Kontaktpads können über die strukturierte Schutzschicht hinausragen.

According to one embodiment, the method comprises the following further steps:

• F) Applying a protective layer to the top side of the sensor element. The protective layer completely covers the top side except for two partial areas. The partial areas are arranged over a flat end area of the electrodes, onto which the contact pads can be applied in the subsequent process step. The protective layer is structured either
  1. (a) applied over the entire surface and the free partial areas are created by a subsequent process such as wet chemical etching or dry etching or laser structuring or
  2. (b) directly applied in a structured manner by using a mask during the deposition process.
• G) Forming contact pads in the areas free of the protective layer for electrically contacting the sensor element. One contact pad is formed directly on a flat end area of each of the electrodes. The contact pads can extend beyond the structured protective layer.

The contact pads can be Cu, Au, Ni, Cr, Ag, Ti, Ta, W, Pd, or Pt. If the sensor element is integrated into a SESUB structure, the contact pads preferably comprise Cu. The contact pads then preferably have a thickness of > 5 µm. The contact pads are designed such that they protrude beyond a surface of the finished sensor element.

As an alternative to contact pads, bumps or thin electrodes can also be used. All of these possible contact elements contain at least one metal, such as Cu, Au, or a solderable alloy.

H) Separating or isolating the sensor elements.

1. (1) Vereinzeln in x-/y- Richtung (Länge & Breite). Dies kann beispielsweise durch Plasmaätzen oder Sägen erfolgen. Der Träger wird hierbei nicht durchgesägt, sondern nur bis auf eine definierte Dicke eingesägt.
2. (2) Vereinzeln in z-Richtung (Höhe). Das Grinding erfolgt von der Rückseite. Durch einen Schleifprozess wird von der Unterseite des Trägers Material bis zu einer definierten finalen Bauteildicke abgetragen.

The separation takes place in two steps:

1. (1) Slicing in the x/y direction (length & width). This can be done, for example, by plasma etching or sawing. The substrate is not sawn through, but only cut to a defined thickness.
2. (2) Singling in the z-direction (height). Grinding takes place from the back side. Material is removed from the underside of the carrier through a grinding process until a defined final component thickness is reached.

I) If a thicker sensor element design is desired, grinding the substrate is not necessary. In this case, separation is achieved solely by sawing or plasma etching.

J) Optional plasma etching of the ground underside of the carrier to reduce, for example, microcracks.

According to one embodiment, the functional material is applied in a structured manner. In other words, the functional layer is structured to adjust the resistance value. The functional layer can have a plurality of stripes. Alternatively, a portion of the functional layer can be stepped, trapezoidal, or triangular. This results in different individual resistances that are connected in parallel between the electrode fingers, thus enabling trimming to the desired target resistance.

According to one embodiment, the electrodes are structured for adjusting the resistance value. The electrode fingers of at least one of the two electrodes can have different lengths. Alternatively or additionally, adjacent electrode fingers can have different spacings from one another. Alternatively or additionally, the electrode fingers can have different shapes. For example, at least one of the electrode fingers is trapezoidal, or at least one of the electrode fingers can have a comb-shaped region. The comb-shaped region can have a plurality of teeth, which preferably point in the direction of the subsequent electrode finger.

The structured design of the electrodes and/or the functional layer creates individual laser-trimmable regions, allowing for resistance adjustment. The corresponding trimming increases the resistance to the target value. The individual trimmable/structured regions have a higher resistance than the non-structured regions. In a parallel circuit, where the individual resistances are added as reciprocals, this means that trimming larger resistances results in a small change in resistance across the entire sensor element. This makes it possible to create a sensor element with a particularly tight resistance tolerance.

The drawings described below are not to be considered to scale. Rather, individual dimensions may be enlarged, reduced, or distorted for clarity.

Elements that are identical or that perform the same function are designated by the same reference symbols.

• 1 eine Explosions-Darstellung eines Sensorelements gemäß dem Stand der Technik,
• 2 eine Schnittdarstellung des Sensorelements nach 1 (Stand der Technik),
• 3a eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem ersten Ausführungsbeispiel,
• 3b eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem weiteren Ausführungsbeispiel,
• 4 eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem weiteren Ausführungsbeispiel,
• 5 eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem weiteren Ausführungsbeispiel,
• 6 eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem weiteren Ausführungsbeispiel,
• 7 eine Draufsicht auf einen Teilbereich eines Sensorelements gemäß einem weiteren Ausführungsbeispiel.

They show:

• 1 an exploded view of a sensor element according to the prior art,
• 2 a sectional view of the sensor element according to 1 (State of the art),
• 3a a plan view of a partial area of a sensor element according to a first embodiment,
• 3b a plan view of a partial area of a sensor element according to a further embodiment,
• 4 a plan view of a partial area of a sensor element according to a further embodiment,
• 5 a plan view of a partial area of a sensor element according to a further embodiment,
• 6 a plan view of a partial area of a sensor element according to a further embodiment,
• 7 a plan view of a partial area of a sensor element according to a further embodiment.

The 1 and 2 show a representation of a sensor element 1 according to the prior art. The sensor element 1 serves to illustrate a basic structure of the sensor element 100 described below. With regard to the essential features of the sensor element 1 according to 1 and 2 will refer to the German patent application DE 10 2020 122 923 A1 Reference is made.

The sensor element 1 is an NTC thin-film temperature sensor and has a carrier 2 with a top side 11 and a bottom side 12. The top side 11 of the carrier 2 has an insulating Layer 3, for example, comprising SiO ₂ . The sensor element 1 further comprises at least two electrodes 4a, 4b. The two electrodes 4a, 4b are formed spaced apart from one another on the insulating layer 3 of the carrier 2 and comprise thin metal films.

The electrodes 4a, 4b are designed as interdigital thin-film electrodes. In particular, the electrodes 4a, 4b each have a flat end region 6 and a region with electrode fingers 5. The region with the electrode fingers 5 is formed in a central region of the carrier 2. The flat end region 6 and the region with the electrode fingers 5 merge into one another. The two electrodes 4a, 4b each interlock in the region of the electrode fingers 5 in the central region of the carrier 2, forming an interdigital structure there. The electrode fingers 5 of the electrodes 4a, 4b are arranged alternately.

The sensor element 1 further comprises a functional layer 7 with a top side 14 and a bottom side 15. The functional layer 7 is an NTC thin film. The functional layer 7 only partially covers the insulating layer 3 on the top side 11 of the carrier 2. Preferably, the functional layer 7 is at least partially applied to the electrodes 4a, 4b. As can be seen from the 1 and 2 As can be seen, the electrodes 4a, 4b are formed between the carrier 2 and the functional layer 7, in particular on an underside 15 of the functional layer 7. The functional layer 7 lies directly on the area with the electrode fingers 5.

The sensor element 1 further comprises at least two contact pads 10a, 10b for electrically contacting the sensor element 1.

The sensor element 1 can further comprise a protective layer 8. The protective layer 8 completely covers a top side of the sensor element 1, with the exception of the contact pads 10a, 10b. The protective layer 8 has recesses 9 from which the contact pads 10a, 10b protrude for electrically contacting the sensor element 1.

Due to the compact design of the individual components of the sensor element 1, the sensor element 1 is ideally suited for integration into MEMS or SESUB structures.

The execution of the basic structure according to the 1 and 2 is based on the principle of a parallel connection of individual resistors. In the construction of the sensor element 1 according to the 1 and 2 However, the resistance cannot be adjusted to the specific component. Therefore, the resistance variation cannot be adjusted within the required tolerances.

The 3a, 3b and 4 to 7 each show a partial area of a sensor element 100. The sensor element 100 has essentially the same components as the sensor element 1 according to the 1 and 2 . The basic structure of the sensor element 100 corresponds to the structure of the sensor element 1 of the 1 and 2 , as already mentioned above. Regarding the details of the components and the functioning of the sensor element 100, please refer to the above description or to the document DE 10 2020 122 923 A1 referred to.

In contrast to sensor element 1, the sensor element 100 can be configured according to the 3 to 7 The resistance can be adjusted component-specifically. This can be achieved through various variants of the layer structure of the sensor element 100, which are described in detail below. In particular, compared to sensor element 1, the structure of the functional layer 7 and/or the electrodes 4a, 4b is adapted/modified. The structured design of the electrodes 4a, 4b and/or the functional layer 7 creates individual laser-trimmable regions, which provide the possibility of adjusting the resistance. An initial resistance of the functional layer 7 is selected such that it lies within the tolerance window for low resistance values. The corresponding trimming increases the resistance to the target value.

The individual trimmable/structured areas have a higher resistance than the non-structured areas of the base structure (sensor element 1). In a parallel circuit, where the individual resistances are added as reciprocals, this means that trimming larger resistances results in a small change in resistance across the entire sensor element 100. Trimming is performed using a suitable laser.

In the embodiment according to 3a The functional layer 7 is structured. In particular, in contrast to the basic structure, the functional layer 7 is structured in such a way that individual strips 7a are formed, which are perpendicular to the electrode fingers 5 and are contacted via them. This results in several individual resistors that are connected in parallel between the electrode fingers 5.

A width b of the strips 7a can be the same for all strips 7a or can vary, so that, for example, (very) narrow, medium and wide strips 7a are combined and thus a greater variance in the resistance setting is given.

Trimming is performed using a laser. It can be performed in two ways. Depending on the type of laser used, either the functional layer 7 (in particular, individual strips 7a of the functional layer 7) or one or more electrode fingers 5 can be severed.

In this embodiment, the electrode fingers 5 can be severed both in the transition region of the electrode fingers 5 to the flat end regions 6 of the electrode 4a, 4b and in a region between the individual strips 7a of the functional layer 7.

In the embodiment according to the 3b Additionally, an electrode finger 5 of one of the electrodes 4a, 4b is structured. In particular, in this exemplary embodiment, an outer electrode finger 5 of the electrode 4a is trapezoidal. Furthermore, several electrode fingers 5 can also be structured, or alternatively or additionally, one of the inner electrode fingers 5 can be structured (not explicitly shown).

The specific design of at least one electrode finger 5 results in an even finer adjustment of the resistance through a wider spread of the trimmable individual resistors between adjacent electrode fingers 5.

Here, too, trimming (depending on the laser used) can be performed by severing individual strips 7a of the functional layer 7 or the electrode fingers 5. The electrode fingers 5 can be severed both in the transition region of the electrode fingers 5 to the flat end regions 6 of the electrode 4a, 4b and in an area between the individual strips 7a of the functional layer 7.

In the embodiment according to 4 The functional layer 7 is structured. In particular, the functional layer 7 has a stepped structure. Alternatively, the functional layer can also be trapezoidal or triangular (not explicitly shown). Unlike in the embodiments described in the 3a and 3b As shown, the functional layer does not have a plurality of discrete individual elements, but is formed in one piece.

Despite the flat design, the functional layer 7 covers only a partial area, in particular partial areas of different sizes, of the individual electrode fingers 5. This results in different individual resistances, which are connected in parallel between the electrode fingers 5 and thus enable trimming to the desired target resistance. Trimming is performed by separating at least one electrode finger 5 using a laser.

In the embodiment according to 5 One of the electrodes 4a, 4b is structured. In particular, the electrode 4a has electrode fingers 5 of different lengths, whereby the structuring can alternatively or additionally also be formed on the electrode 4b.

The 5 The electrode finger shown at the very bottom (lower outer electrode finger 5) is the shortest electrode finger 5. The 5 The electrode finger shown at the very top (upper outer electrode finger 5) is the longest electrode finger 5. Of course, another electrode finger 5, for example, a middle electrode finger 5, can also be shorter or longer than the other electrode fingers 5. In other words, the length of the electrode fingers 5 as well as the arrangement of the different length electrode fingers 5 can be freely selected, depending on the desired resistance value.

In this embodiment, the functional layer 7 is formed flat or rectangular analogously to the one used in connection with the 1 and 2 described basic structure.

The different lengths of the electrode fingers 5 result in different individual resistances, which are connected in parallel between the electrode fingers 5 and thus enable trimming to the desired target resistance.

Here, too, trimming is performed by cutting at least one electrode finger 5 using a laser. Unlike the embodiments with a structured functional layer 7, cutting the electrode fingers 5 is only possible in the transition area between the electrode fingers 5 and the flat end regions 6 of the electrodes 4a, 4b (the area of the electrode fingers 5 not covered by the functional layer 7).

In the embodiment according to 6 The electrode fingers 5 have different distances from one another. In particular, the specific design of the electrodes 4a, 4b allows a distance A between adjacent electrode fingers 5 to be varied.

Thus, the electrode fingers 5, which are in 6 shown below, have a greater distance A between each other than the other electrode fingers 5. This design is not limited to this specific embodiment, but the distance A between adjacent electrodes The distance A between the electrode fingers 5 can be increased or decreased as desired, depending on the desired resistance values. The distance A between just one adjacent pair of electrode fingers or between multiple pairs of electrode fingers can be varied.

This special design allows for additional trimming areas with varying distances, providing the option for even finer resistance adjustment.

In the embodiment according to 7 At least one electrode finger 5 is structured. In particular, one electrode finger 5 (in this exemplary embodiment, an outer electrode finger 5 of the electrode 4b) has a comb-shaped region. However, a corresponding comb-shaped region can also be provided on further or other outer electrode fingers 5 (not explicitly shown).

The comb-shaped region has a plurality of teeth 20. These point toward the subsequent electrode finger 5. The teeth 20 are designed with different lengths. Alternatively or additionally, the teeth 20 can also be designed with different widths.

The functional layer 7 does not extend completely over the structured electrode finger 5, as can be seen from 7 Rather, the functional layer 7 only partially covers the structured electrode finger 5. In this exemplary embodiment, the functional layer can also be made even wider and extend in particular up to the flat end regions 6 and even partially over the flat end regions 6 of the electrodes 4a, 4b (see functional layer 22 indicated by dashed lines).

The comb-shaped structured area of the electrode finger 5 allows for greater variance in the resistance setting. This results in different individual resistances, which allow trimming to the desired target resistance. Trimming is achieved by cutting the structured electrode finger 5 with the aid of a laser (see example cutting area 21).

A method for producing the sensor element 100 is described below. Preferably, the method produces a plurality of sensor elements 100 according to one of the embodiments described above (see 3a, 3b and 4 to 7 ). All features described in connection with the sensor element 100 therefore also apply to the method, and vice versa.

In a first step A), a carrier material is provided for forming the carrier 2 described above. The carrier material preferably comprises Si, SiC, GaN, or glass. Alternatively, the carrier material may comprise Si ₃ N ₄ , AlN, or Al ₂ O ₃ . The carrier 2 has a top side 11 and a bottom side 12. The carrier 2 preferably has a maximum edge length L of less than 500 µm.

Subsequently, an electrically insulating layer 3 is formed on the top side 11 of the carrier 2. For example, the insulating layer 3 comprises SiO ₂ . Ideally, an insulating layer 3 with a thickness of up to 1.5 µm is produced on the top side 11 of the carrier 2.

In a further step B), at least two electrodes 4a, 4b are formed/deposited on the carrier 2. The deposition is carried out by a PVD or CVD process or galvanically.

The electrodes 4a, 4b can be single-layer or multi-layer and comprise, for example, Cu, Au, Ni, Cr, Ag, Ti, Ta, W, Pd, or Pt. The electrodes 4a, 4b are designed as thin-film electrodes. The electrodes 4a, 4b each have a flat end region 6 and a plurality of electrode fingers 5.

The structuring of the electrodes 4a, 4b takes place in a subsequent process, which can be, for example, wet-chemical etching, dry etching, or laser structuring. The electrode fingers 5 of at least one of the two electrodes 4a, 4b can have a different length ( 5 ). Alternatively or additionally, adjacent electrode fingers 5 can have a different distance A from each other ( 6 ). Alternatively or additionally, the electrode fingers 5 can have a different shape ( 3b , 7 ). For example, at least one of the electrode fingers 5 is trapezoidal or stepped, or at least one of the electrode fingers 5 can have a comb-shaped region with teeth 20. The structuring creates a laser-trimmable region for adjusting the resistance value of the sensor element 100. Additionally or alternatively, the functional layer 7 can also have a structuring ( 3a , 3b , 4 ).

In a further step C), a functional material is applied to form a functional layer 7.

This is done, for example, by sputtering or a spin coating process. The functional material is first applied over the entire surface and then, in a further process (for example, by wet chemical etching or dry etching or laser structuring). The functional layer 7 preferably has a thickness between 250 nm and 400 nm.

Alternatively, step C) can also be carried out before step B), so that the functional material 7 is sputtered directly onto the insulating layer 3 of the carrier 2 and then the electrodes 4a, 4b are applied to the functional layer 7.

The functional material comprises an NTC ceramic based on an oxide material with a perovskite or spinel structure. Alternatively, the functional material can also be based on a carbide or nitride material. In another alternative, the functional material comprises or consists of thin films of vanadium oxide or SiC.

The functional layer 7 only partially covers the upper side of the carrier 2 or the electrodes 4a, 4b. The functional layer 7 can be structured to adjust the resistance value of the sensor element 100. The functional layer 7 can, for example, be formed in a strip shape ( 3a , 3b) Alternatively, the functional layer 7 can be designed in a stepped, trapezoidal or triangular shape ( 4 This results in different individual resistances connected in parallel between the electrode fingers 5, thus enabling trimming to the desired target resistance. The initial resistance of the functional layer 7 is selected such that it lies within the tolerance window for low resistance values.

In a further step D), the functional layer 7 is subjected to a heat treatment to form the structure or properties.

Subsequently, functional layer 7 is measured. This determines the initial resistance value so that the resistance can be adjusted to the desired value in the next step.

In a next step E), the resistance value is adjusted by trimming at least one of the electrodes 4a, 4b and/or the functional layer 7 using a laser. Trimming is preferably performed in situ.

The resistance value is set to a predetermined nominal value (target value). By precisely adjusting the resistance value, the finished sensor element 100 has a very tight resistance tolerance. To adjust the resistance value, at least one of the electrode fingers 5 and/or at least a portion of the functional layer 7 is severed using the laser. In particular, the previously described structured regions are severed.

In a next step F), a protective layer 8 is formed. The protective layer 8 can comprise oxides, nitrides, ceramics, glasses, or polymers and is produced using a PVD or CVD process and structured using wet-chemical etching or dry etching. The protective layer 8 has a thickness of <10 µm, preferably <5 µm, particularly preferably <1 µm. Ideally, the protective layer 8 has a thickness of <1.5 µm and completely covers the upper side of the sensor element 100, with the exception of the contact pads 10a, 10b.

Subsequently, in step G), contact pads 10a, 10b are formed on at least a portion of the electrodes 4a, 4b. One contact pad 10a, 10b is formed directly on the flat end region 6 of each electrode 4a, 4b. In one embodiment, the contact pads 10a, 10b comprise metals such as Cu, Al, or Au and have a thickness of > 5 µm. In particular, the contact pads 10a, 10b protrude above the surface 13 of the sensor element 100 in the finished sensor element 100. Alternatively, bumps can be formed instead of the contact pads.

In a further step H), the sensor elements 100 are separated. This can be done, for example, by plasma etching or sawing. The carrier 2 is not sawn through, but only cut to a defined thickness.

Through subsequent optional grinding from the back side (a grinding process), material is removed from the back side of the carrier 2 down to a defined final component thickness in a final step I). This step results in the actual separation of the sensor elements 100. If a thicker design of the sensor element 100 is desired, step I) can also be omitted. In this case, the separation of the sensor elements 100 is carried out solely by sawing or plasma etching.

The description of the objects specified here is not limited to the individual specific embodiments. Rather, the features of the individual embodiments can be combined with one another in any way—as far as technically feasible.

List of reference symbols

1, 100

Sensor element

2

carrier

3

Insulating layer

4a,b

electrode

5

Electrode finger

6

End area

7

Functional layer

7a

stripes

8

protective layer

9

recess

10a,b

Contact pad

11

Top of the carrier

12

Underside of the carrier

13

Surface of the sensor element

14

Top of the functional layer

15

Underside of the functional layer

20

Tooth

21

Separation area

22

Functional layer

D

Thickness of the sensor element

L

Edge length of the carrier

A

Distance between adjacent electrode fingers

b

Width of the stripes

Claims (33)

Sensor element (100) for measuring a temperature, comprising - at least one carrier (2) with a top side (11) and a bottom side (12), wherein an electrically insulating layer (3) is formed on the top side (11) of the carrier (12), wherein the electrically insulating layer (3) completely covers the top side (11) of the carrier (2), - at least one functional layer (7) comprising a material with a temperature-dependent electrical resistance, wherein the functional layer (7) is arranged on the electrically insulating layer (3), - at least two electrodes (4a, 4b) which are formed spaced apart from one another on the carrier (2), wherein the respective electrode (4a, 4b) has a plurality of electrode fingers (5), wherein the electrode fingers (5) of the two electrodes (4a, 4b) are arranged alternately with one another, and wherein at least one of the electrode fingers (5) has a comb-shaped region, wherein the comb-shaped region has a plurality of teeth (20) which extend in the direction of the subsequent electrode finger (5), and wherein at least one of the electrode fingers (5) has a different shape than the remaining electrode fingers, and wherein the at least one electrode finger (5) is trapezoidal or triangular, - at least two contact pads (10a, 10b) for electrically contacting the sensor element (100), wherein each contact pad (10a, 10b) is arranged directly on a partial area of one of the electrodes (4a, 4b), wherein the sensor element (100) has a maximum edge length of < 500 µm and a thickness of < 50 µm, wherein the sensor element (100) is designed to be integrated directly into an electrical system as a discrete component, wherein the sensor element (100) is designed for direct integration into a MEMS structure and/or into a SESUB structure, wherein the sensor element (100) has a narrow resistance tolerance. Sensor element (100) according to Claim 1 , wherein the at least one functional layer (7) and/or at least one of the at least two electrodes (4a, 4b) are structured for adjusting the resistance value. Sensor element (100) according to Claim 1 or 2 , wherein the comb-shaped region is formed on one of the outer electrode fingers (5). Sensor element (100) according to one of the preceding claims, wherein the teeth (20) are of different lengths and/or different widths. Sensor element (100) according to one of the preceding claims, wherein, in order to adjust the resistance value of the sensor element (100), at least a partial region of the electrode finger (5) is severed with the comb-shaped region. Sensor element (100) according to one of the preceding claims, wherein the functional layer (7) only partially covers the electrode fingers (5). Sensor element (100) according to one of the preceding claims, wherein the functional layer (7) has a plurality of strips (7a) which are arranged spaced apart and parallel to one another on the upper side (11) of the carrier (2). Sensor element (100) according to Claim 7 , wherein the strips (7a) are formed perpendicular to the electrode fingers (5) and are contacted via them. Sensor element according to one of the Claims 7 or 8 , wherein a width (b) of the strips (7a) is the same for all strips (7a) or wherein a width (b) of the strips (7a) varies. Sensor element according to one of the Claims 7 until 9 , wherein at least a partial area of a strip (7a) and/or at least a partial area of an electrode finger (5) is severed in order to adjust the resistance value of the sensor element (100). Sensor element (100) according to one of the Claims 1 until 6 , wherein the functional layer (7) is stepped, trapezoidal or triangular. Sensor element (100) according to Claim 11 , wherein at least one electrode finger (5) is severed to adjust the resistance value. Sensor element (100) according to one of the preceding claims, wherein the electrode fingers (5) of at least one of the at least two electrodes (4a, 4b) are of different lengths. Sensor element (100) according to Claim 13 , wherein at least one of the electrode fingers (5) of different lengths is severed in order to adjust the resistance value. Sensor element (100) according to one of the preceding claims, wherein a distance (A) between adjacent electrode fingers (5) varies. Sensor element (100) according to one of the preceding claims, wherein the respective electrode (4a, 4b) is designed as a thin-film electrode. Sensor element (100) according to one of the preceding claims, wherein the functional layer (7) is a thin film with NTC characteristics. Sensor element (100) according to one of the preceding claims, wherein the carrier (2) comprises silicon, silicon carbide or glass or wherein the carrier (2) comprises Si ₃ N ₄ , AlN, GaN or Al ₂ O ₃ as carrier material. Sensor element (100) according to one of the preceding claims, wherein the functional layer (7) comprises an NTC ceramic based on an oxidic material in the perovskite or spinel structure type or wherein the functional layer (7) comprises an NTC ceramic based on a carbide or a nitride material. Sensor element (100) according to one of the preceding claims, wherein the electrodes (4a, 4b) are formed in a single layer or in multiple layers and comprise at least one material or a material combination of Cu, Au, Ni, Cr, Ag, Ti, Ta, W, Pd and/or Pt. Sensor element (100) according to one of the preceding claims, wherein the contact pads (10a, 10b) are formed in a single layer or in multiple layers and comprise at least one material or a material combination of Cu, Au, Ni, Cr, Ag, Ti, Ta, W, Pd and/or Pt. Sensor element (100) according to one of the preceding claims, wherein the insulating layer (3) is formed in a single layer or in multiple layers and comprises Al ₂ O ₃ , AlN, SiO ₂ or Si ₃ N ₄ or combinations of layers of these materials. Sensor element (100) according to one of the preceding claims, further comprising a protective layer (8), wherein the protective layer (8) completely covers an upper side of the sensor element (100) with the exception of the contact pads (10a, 10b). Sensor element (100) according to Claim 23 , wherein the protective layer (8) is formed in a single layer or in multiple layers and comprises Al ₂ O ₃ , AlN, SiO ₂ or Si ₃ N ₄ or combinations of layers of these materials. Sensor element (100) according to Claim 23 or 24 , wherein the protective layer (8) comprises oxides, nitrides, ceramics, glasses or plastic as material. A method for producing a sensor element (100) according to one of the preceding claims, comprising the following steps: A) Providing a carrier material with an insulating layer (3) for forming a carrier (2); B) Forming at least two electrodes (4a, 4b) on the carrier (2), wherein each electrode (4a, 4b) has a plurality of electrode fingers (5), wherein the electrode fingers (5) of the two electrodes (4a, 4b) are arranged alternately with each other, wherein at least one of the electrode fingers (5) has a comb-shaped region, wherein the comb-shaped region has a plurality of teeth (20) pointing in the direction of the subsequent electrode finger (5), and wherein the electrode fingers (5) have a different shape, wherein at least one of the electrode fingers (5) is trapezoidal or triangular; C) Applying a functional material to a partial region of the electrodes (4a, 4b) to form a functional layer (7); D) Temperature treatment of the functional layer (7); E) Adjustment of the resistance value by trimming at least a portion of the electrodes (4a, 4b) and/or the functional layer (7) using a laser. Procedure according to Claim 26 , wherein the functional layer (7) and/or at least one of the electrodes (4a, 4b) is structured and wherein an initial resistance of the functional layer (7) is selected such that it is located in a tolerance window at low resistance values, wherein a resistance of the sensor element (100) is increased to a desired value by trimming the structured regions. Procedure according to Claim 26 or 27 , wherein in step E) at least a partial area of the electrode fingers (5) and/or at least a partial area of the functional layer (7) are severed in order to adjust the resistance value. Method according to one of the Claims 26 until 28 , wherein before step E) the functional layer (7) is measured. Procedure according to one of the Claims 26 until 29 , further comprising the following steps: F) applying a protective layer (8) to an upper side of the sensor element (100), wherein the protective layer (8) completely covers the upper side except for two partial areas; G) forming contact pads (10a, 10b) in the partial areas free of the protective layer for electrically contacting the sensor element (100); H) separating the sensor elements (100). Method according to one of the Claims 26 until 30 , comprising the further steps: I) optional grinding of the sensor elements (100) from an underside, wherein material is removed from the back of the carrier (2) by a grinding process up to a defined final component thickness, whereby the sensor elements (100) are separated; J) optional plasma etching of the ground-down underside of the carrier (2) to reduce microcracks. Method according to one of the Claims 26 until 31 , wherein the functional layer (7) has a plurality of strips (7a) or wherein the functional layer (7) is formed in a stepped, trapezoidal or triangular manner. Procedure according to one of the Claims 26 until 32 , wherein the electrode fingers (5) of at least one of the two electrodes (4a, 4b) have a different length and/or wherein adjacent electrode fingers (5) have a different distance (A) from one another.