CN1203312C - Capacitance type relative humidity sensor - Google Patents

Abstract

The present invention relates to a capacitor type relative humidity sensor used for humidity signal sensing. The present invention is composed of a substrate, an oxidizing layer and a capacitor electrode, wherein the oxidizing layer is arranged on the substrate; the capacitor electrode is arranged above the oxidizing layer; a contact conductor is arranged on the capacitor electrode; the capacitor electrode is an electrode with the materials which are suitable for the standard CMOS processing technology; a passivation layer is arranged on the capacitor electrode. The present invention uses a parallel structure in an aluminum electrode comb shape, so a sensitive capacitance value is increased. The substrate is in a reliable grounding state, so the outside interference is eliminated, and the accuracy of the humidity sensor is improved. Because of the sedimentation of the passivation layer, aluminium electrode corrosion by water vapor in polyimide in water vapor, particularly polyimide after water absorption in environment can be effectively avoided, and the reliability is improved. Comb-shaped parallel polysilicon is used as a heating circuit, so the desorption time of the humidity sensor is short, and the reliability is improved. Polyimide is used as a humidity sensing medium, so the present invention has the advantages of high sensitivity, high linearity, good hysteresis loop performance, long-term reliability, etc.

Description

Capacitive relative humidity sensor

1. Technical field

The invention relates to a micromechanical sensor, in particular to a capacitive relative humidity sensor.

2. Background technology

At present, most of the practical applications in environmental testing are traditional humidity sensors, such as dry bulb hygrometers and dew point hygrometers. These humidity sensors have the following disadvantages: (1) poor consistency of the same product; (2) expensive; (3) large in size; (4) poor linearity and hysteresis characteristics, and sometimes need to look up the table during measurement. The capacitive relative humidity sensor compatible with CMOS (CMOS is a well-known technical term in the art) technology is a kind of micro humidity sensor, which has the advantages of small size, low price and good product consistency. In 1990, H.Baltes (person's name) first proposed the use of CMOS technology to manufacture humidity sensors. The humidity sensor uses air as the humidity-sensing medium. Due to the influence of surface adsorption, the linearity and hysteresis characteristics are very poor, and the accuracy is very low. And because the aluminum electrode is exposed to the air and is easily corroded by water vapor, the reliability is relatively poor. In 1991, Boltshauser (personal name) used CMOS technology and post-processing technology to make a relative capacitive humidity sensor using polyimide as a moisture-sensing medium. The electrodes of this humidity sensor and polyimide directly contact polyimide for adsorption After water vapor will corrode the aluminum electrode, the reliability is low, and the impurities attached to the surface are difficult to remove after long-term use. In 2000, Uksong Kang (personal name) gave a high-speed humidity sensor. In this structure, there are two layers of insulating silicon dioxide and a layer of sensitive electrode heat insulation on the polysilicon used for heating, and the heating effect is poor; the structure It is more complicated and cannot be completed by a standard CMOS process. And the electrode is exposed in the air, in order to prevent the corrosion of water vapor in the air, the selection of the electrode is limited, and the long-term reliability is poor. Some of the above humidity sensors cannot meet the requirements of long-term reliability and short desorption time, and are easily affected by the external environment.

3. Contents of the invention

Technical problem: The present invention provides a high-precision capacitive relative humidity sensor that can improve its reliability.

Technical solution: The present invention is a capacitive relative humidity sensor for humidity signal sensing, which is composed of a substrate, an oxide layer, and a capacitor electrode. The oxide layer is arranged on the substrate, and the capacitor electrode is arranged above the oxide layer. Electrode leads are arranged on the electrodes, and the capacitor electrodes are electrodes whose material is suitable for standard CMOS processing technology, and a passivation layer is arranged on the capacitor electrodes.

Technical effect: the process steps of the present invention are simple, can be manufactured by standard CMOS process, has high precision and good long-term reliability. The aluminum electrode comb-like parallel structure can increase the sensitive capacitance value, reliably ground the substrate to eliminate external interference, and improve the accuracy of the humidity sensor. Depositing the passivation layer can effectively prevent water vapor in the environment, especially after the polyimide absorbs water, the water vapor in the polyimide corrodes the aluminum electrode, thereby improving reliability. Comb-shaped parallel polysilicon is used as a heating circuit to heat evenly, effectively remove volatile impurities on the surface of the humidity sensor, shorten the desorption time of the humidity sensor, and also improve reliability. Polyimide is set between the capacitor electrodes, and the upper surface of the oxide strip is higher than the upper surface of the polycrystalline strip, which reduces the edge effect between the aluminum electrode and the silicon dioxide layer, improves linearity, reduces parasitic capacitance, and thus improves accuracy . Utilizing polyimide as the humidity-sensitive medium has the advantages of high sensitivity, good linearity and hysteresis characteristics, long-term reliability, etc., and the structural setting of the invention makes it compatible with standard CMOS processing technology.

4. Description of drawings

Fig. 1 is a schematic structural view of the present invention.

Figure 2 is a top view of the present invention.

Fig. 3 is a schematic diagram of the comb-shaped electrode structure of the present invention.

Fig. 4 is a schematic diagram of the structure of a comb-shaped parallel polysilicon layer according to the present invention.

5. Specific implementation

The present invention is a capacitive relative humidity sensor for humidity signal sensing, which consists of a substrate 106, an oxide layer 104, and capacitor electrodes 101 and 102. The oxide layer 104 is arranged on the substrate 106, and the capacitor electrodes 101 and 102 are arranged Above the oxide layer 104, electrode leads 1011 and 1021 are provided on the capacitor electrodes 101 and 102. The capacitor electrodes 101 and 102 are electrodes whose material is suitable for standard CMOS processing technology. Passivation is provided on the capacitor electrodes 101 and 102. layer 108, a moisture-sensing medium layer 107 is provided between and above the capacitor electrodes 101 and 102, the passivation layer 108 is located between the capacitor electrodes 101 and 102 and the moisture-sensing medium layer 107, and between the capacitor electrodes 101 and 102 and the oxide layer A silicon dioxide strip 105 is provided between 104 and the upper surface of the silicon dioxide strip 105 is higher than the lower surface 1071 of the moisture-sensitive medium layer 1071, and a heating strip 103 is provided between the moisture-sensitive medium layer 107 and the oxide layer 104, specifically In other words, the heating strip 103 can be arranged between the lower surface 1071 of the moisture-sensitive medium layer 107 and the oxide layer 104, or the heating strip 103 can be arranged between the silicon dioxide strip 105 and the oxide layer 104. 103 is provided with heating strip leads 1031 and 1032, and a silicon nitride layer 1081 is provided between the moisture-sensitive medium layer 107 and the heating strip 103. The passivation layer 108 of this embodiment is a silicon nitride layer, and the passivation layer 108 It is also possible to adopt a technical measure consisting of a silicon dioxide layer and a silicon nitride layer, and the silicon nitride layer is arranged on the top of the silicon dioxide layer. The capacitor electrodes 101 and 102 are comb-shaped electrodes and are arranged alternately. The moisture-sensitive medium layer 107 is Polyimide layer, the heating strip 103 is a comb-shaped parallel polysilicon layer, the substrate 106 is grounded, the capacitor electrodes 101 and 102 are aluminum electrodes, and the capacitor electrodes 101 and 102 can also be gold electrodes or polysilicon electrodes, the moisture-sensitive medium of the present invention Due to changes in the relative humidity of the external environment, the adsorption/desorption of water vapor molecules in the air causes the dielectric constant of the humidity-sensing medium to change, causing the capacitance value of the humidity sensor to change. There is a definite relationship between relative humidity and sensitive capacitance. When the relative humidity of the environment increases, the capacitance value of the humidity sensor increases, and when the relative humidity of the environment decreases, the capacitance value of the humidity sensor decreases accordingly. The output terminal of the humidity sensor is connected to the peripheral circuit, and the sensitive capacitance value passes through the interface circuit.

To convert it into a measurable electrical signal (such as voltage, current), the present invention can be produced by using the following processes: growing a thin oxide layer 104 on a silicon substrate, depositing polysilicon 103, and photoetching into a comb-shaped parallel S-type , CVD deposits silicon dioxide 105, exposes polysilicon 103 by photolithography, deposits 1 micron aluminum, and forms comb electrodes 101, 102 by photolithography (removing aluminum on polysilicon). Next, silicon nitride 108 is deposited as a passivation layer, and polyimide (107) with a thickness of about 1.5 microns is coated by spin coating, and the thickness of polyimide (107) after photolithography and imidization is about 1 Microns. The bipolar plates of the humidity sensor (take the aluminum electrode as an example), the aluminum electrode plates are respectively composed of 21 strip-shaped aluminum electrodes with a width of 3 microns and a length of 400 microns in a comb structure, and the distance between adjacent plates is 4 microns. The heating polysilicon structure is shown in Figure 4. The polysilicon 103 adopts a comb-shaped parallel S-shaped structure, which is conducive to uniform heating. Each polysilicon strip (103) is 450 microns long, 3 microns wide, and 3500 angstroms thick. 14 polysilicon strips are connected in parallel. , and then connected in series, the total resistance is about 1.5KΩ, the thickness of silicon nitride as the passivation layer 108 is 3000 angstroms, in order to prevent the aluminum electrodes 101, 102 from being corroded by the moisture absorbed by the polyimide 107, the polyimide 107 The thickness is about 1 micron. In FIG. 2, the aluminum electrode 109 is grounded to eliminate the influence of the outside world on the sensitive capacitance. The polysilicon strip is a heating circuit, and the aluminum electrodes 101 and 102 output capacitance signals. The ambient relative humidity measurement range is 0%RH to 100%RH, and the temperature range is -40°C to 60°C.

Claims (7)

1. A capacitive relative humidity sensor for humidity signal sensing, consisting of a substrate (106), an oxide layer (104), capacitor electrodes (101 and 102), and the oxide layer (104) is located on the substrate (106) ), the capacitive electrodes (101 and 102) are arranged above the oxide layer (104), and the electrode leads (1011 and 1021) are arranged on the capacitive electrodes (101 and 102), and the capacitive electrodes (101 and 102) are suitable for their materials An electrode based on a standard CMOS processing technology is characterized in that a passivation layer (108) is provided on the capacitor electrodes (101 and 102), and a moisture-sensitive dielectric layer (107) is provided between and above the capacitor electrodes (101 and 102) ), the passivation layer (108) is located between the capacitor electrodes (101 and 102) and the moisture-sensitive medium layer (107), and a silicon dioxide strip ( 105) and the upper surface of the silicon dioxide strip (105) is higher than the lower surface (1071) of the moisture-sensitive medium layer (107), and a heating strip (103) is provided between the passivation layer (108) and the oxide layer (104). ), heating strip leads (1031 and 1032) are provided on the heating strip (103), and the heating strip (103) is a polysilicon heating strip. 2. The capacitive relative humidity sensor according to claim 1, characterized in that the passivation layer (108) is a silicon nitride layer. 3. The capacitive relative humidity sensor according to claim 1, characterized in that the passivation layer (108) is composed of a silicon dioxide layer and a silicon nitride layer, and the silicon nitride layer is arranged above the silicon dioxide layer. 4. The capacitive relative humidity sensor according to claim 1, 2 or 3, characterized in that the capacitive electrodes (101 and 102) are comb-shaped electrodes arranged alternately. 5. The capacitive relative humidity sensor according to claim 4, characterized in that the moisture-sensing medium layer (107) is a polyimide layer. 6. The capacitive relative humidity sensor according to claim 1, characterized in that the capacitive electrodes (101 and 102) are aluminum electrodes. 7. The capacitive relative humidity sensor according to claim 1, characterized in that the substrate (106) is grounded.

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