WO2006021612A1

WO2006021612A1 - Micro mechanical clutch and a component integrated thereto

Info

Publication number: WO2006021612A1
Application number: PCT/FI2005/000363
Authority: WO
Inventors: Sami MYLLYMÄKI; Eero Ristolainen
Original assignee: RISTOLAINEN NOORA; RISTOLAINEN PAULA; ZIPIC Oy
Current assignee: RISTOLAINEN NOORA; RISTOLAINEN PAULA; ZIPIC Oy
Priority date: 2004-08-24
Filing date: 2005-08-24
Publication date: 2006-03-02
Anticipated expiration: 2007-02-24
Also published as: FI20041106L; FI20041106A7; FI20041106A0

Abstract

A micro-mechanical clutch. The clutch comprises a clutch built on semiconductor film (100) and a component (110) built at least partly overlapping it and integrated with it. To the area, the motion of which is caused by the clutch, a voltage signal resulting in the change of the clutch position so that moving level (104) rests on supports (102) built for it. The change of position produces a change of charge in the integrated component, as result of which the current changes. The clutch can be made in the same semiconductor layer as the SOI-microcircuits.

Description

Micro-mechanical clutch and a component integrated thereto

Field of invention The invention relates to micro-mechanical components and especially achievement of a micro-mechanical clutch.

Background of invention

In recent years systems comprising micro-mechanical components have become general and commercial. Usually different micro techniques can be called micro system technique (MST), which can for instance be defined as technique by means of which different miniature size mechanical, electronic, optical and other components are assembled and made working unites. Typically, the micro system comprises at least one part, the dimensions of which are of micro-meter class. For instance, the micro systems can be divided into micro-electromechanical systems (MEMS), micro-optoelectro- mechanical systems (MOEMS) and micro-fluidics.

Typically, micro-mechanical systems are based on thin film based surface micro-mechanics. Usually, by means of physical and chemical coating methods amorphous or polycrystalline thin films are grown on the silicon wafer, on which then micro-mechanical structure are formed by means of etching techniques typically used for production of integrated circuits. Typically the moving films of micro-mechanical components are made either of single crystal silicon or of polycrystalline silicon. The film can be made movable so that typically there is under the film a thin insulating layer, which can be corroded off through openings in the silicon film. Generally, today the most used techniques of surface micro-mechanics is so called SOI-micro-mechanics (Silicon-on-Insulator), where on the silicon wafer, working as surface basis, a thin single crystal silicon layer is made so that between them a quite thin insulating oxide coating remains. Then for instance the thickness of the silicon bed can be about 50 - 500 μm, the thickness of the oxide coating 25 -200 nm, the thickness of the of the silicon layer about 30-200 nm. A silicon wafer structure like this is typically most suited as raw material for different micro-mechanical components, since thus an above presented etched oxide coating is completed, on which there is a single crystal silicon layer, the mechanical properties of which are of higher quality than those of. polycrystalline silicon. An important application object of micro-mechanics includes wireless equipment and systems of data communications, such as mobile stations and broadband nets Especially by wireless communication and systems there is need for different first- rate clutches, by means of which it is possible to realise new kinds of transmitter and receiver architectures. Mcro-mechanical components have a small surface area and by means of them the power consumption of portable communications equipment can be significantly reduced. Furthermore, since the micro-mechanical components improve the capacity of equipment, as much capacity as before cannot be required from traditional components. Accordingly, an apparatus essentially more profitable as to its cost structure is achieved. By means of micro-mechanical components the capacity of radio apparatus can also be essentially improved, for instance the sensitivity to noise and to the radius of operation.

There are, however, in micro-mechanical clutches in accordance with present technique many problems. Micro-mechanical clutches are typically considered as fully opening and fully closing clutches, while by means of them it is possible to carry out also other kinds of functions, which bring the components new added value and objects of application.

In present micro-mechanical clutches there are two states, in one of which the clutch is open in regard to the signal direction, i.e. it does not conduct current and in the other one the clutch is shorted out, i.e. it conducts current. Then the impedance of the clutch states separate strongly from each other and the impedance between the states cannot be chosen as clutch state. The feature restricts the use of clutch in a situation, where a smaller surface area for motion is expected than these extremities. As a solution it has been necessary to take an additional component into use, which together with the present clutch has formed the function expected.

Integration of different components with the micro-mechanical clutch has been difficult, since quite hard mechanical stress is directed on the clutch in a situation, where the clutch is closed. Then usually the signal line of the clutch is in direct contact with the movable part, which causes considerable mechanical wear after a relatively short time of use.

Manufacture of separate clutches and of separate components joined to them has been more worth due to better efficiency of the manufacturing processes. However, it has been a must to connect the individual components either with a so called flip-chip joint to the microcircuit or to a separate basis together with the microcircuit. Further, this connected solution is also joined to other electronics of the equipment, which makes the embodiment uncertain due to several joints. In the joints for instance pin joints, ball joints or wire joints are used, which increase the parasite elements of the system. This reduces the operating life oft he equipment and worsens the best elements of the system. This reduces the operating life of achievable technical properties.

Using separate clutches and components relatively much area is needed, which is the total of the surface area of the components in all, of the surface area of the wiring between components and of the surface area to be left for manufacturing technical reason between components. Usually, minimizing this total surface is complicated and can cause functional problems to the components.

Using separate clutches and components the problem is that in regard to the signals they function at different moment. Thereby they cannot have functions, dependent on each other, which take place at the same moment, i.e. in spite of the state of the clutch the component connected to it can function in all its states. Further, components functioning in in different time order are slower, because in regard to the signal they function one after another.

Using a separate component makes it is possible to achieve as electrode spacing of the component about 50 - 200 mm in its minimum due to restrictions by manufacturing technique. Reduction of electrode spacing is quite expensive and by manufacturing technique quite complicated. Furthermore, the properties of some components deteriorate by use of such a small spacing. Due to the restriction of electrode spacing the levels of impedance remain too high and must be made smaller using the level of operating voltage. That results in loss of power on fitting the impedance and increasing leakage currents.

Short presentation of invention

The object of the invention is to develop a micro-mechanical clutch and another component integrated with it so that above presented disadvantages can be reduced. The aims of the invention are reached by the micro-mechanical clutch and the component integrated with it, which are characterized in that what is told in the independent claims. The advantageous embodiments of the invention are the object of the independent claims. The invention is based on the fact that the micro-mechanical clutch can be connected to two states, where both of them leave the clutch open. The first state is the normal state of the clutch, where the capacitance of clutch visible to the signal path is small. The other state is the activated state of the clutch, where the capacitance of clutch visible to the signal path is large. In the invention the other component integrated with the clutch is placed in the same semiconductor layer as the clutch and at least partly overlapping it so that the capacitance changes in the same way and in same step as the capacitance of the clutch. According to an advantageous embodiment of the invention the position of the clutch is changed electrostatically in causing difference of voltage between the electrodes of the clutch. .According to an advantageous embodiment the dead clutch is in the state of low capacitance and the active clutch is in the state of high capacitance. Further, in chancing the position of the clutch the mechanical state of clutch moves and causes a change of distance between the electrodes of the clutch.

According to an advantageous embodiment of the invention the micro- mechanical clutch has common or separate ports for a signal to the integrated component and for a control signal, which determines the state of clutch.

According to an advantageous embodiment of the invention the mechanically moving level of the clutch is supported by one or several insulating supports, which prevent mechanical and electric contact of electrodes. Furthermore, according to an advantageous embodiment the component integrated with the clutch is placed on the area of the moving level or onto it so that the component is influenced by the same change of level distance as the clutch. According to an advantageous embodiment in the SOI-structure, comprising substrate, an insulating oxide coating and topmost a semiconductor layer, the micro- mechanical clutch, the support of the clutch moving level and a component integrated with the clutch are formed. According to an advantageous embodiment the said semiconductor layer is of silicon, silicon germanium or some other semiconductor used in thin film applications. Further according to an advantageous embodiment of the invention the semiconductor layer has a thickness of essentially 50 - 200 nm and advantageously 70 -100 nm.

An advantage of the micro-mechanical clutch according to the invention is that it is possible to reach a small electrode spacing and a high capacitance. Thus the impedance visible in the clutch is small and the power needed by the component reduces. Furthermore, an advantage is that the micro-mechanical clutch can be made large sized so that the electrostatic power it requires can be brought forth by small voltage. Neither does the component integrated with the clutch at the same time need much voltage, since it has been possible to get small electrode pacing with the clutch.

An advantage of the micro-mechanical clutch according to the invention is that the clutch can be used as connecting component on a structure to be piled on the SOI-structure or in the chip by joining. Then the moving level of the clutch moves in the direction of the structure to be piled and the capacitance from SOI-structure or into chip grows remarkably and thus connects the signal without any papillas and balls. Further, the advantage of the clutch according to the invention is that it can be built in the same semiconductor layer as the SOI-microcircuits. Thus the efficiency of the process of manufacture can be increased and the joints in regard to other components become more reliable. Further, an advantage is that the function of the micro-mechanical clutch and the resonator integrated with it takes place simultaneously. This means that with the clutch in a state of high capacitance the impedance of resonator is high and can thus not conduct any current. Further, with the clutch in a state of low capacitance the impedance of resonator is high and can therefore not conduct any current. Further, with the clutch in a state of high capacitance the impedance of resonator is low and can therefore be used with lower voltage than before.

Short presentation of figures

The invention is disclosed now in connection with advantageous embodiments with reference to enclosed figures, where:

Figures Ia, Ib and Ic show the structure of a micro-mechanical clutch according to the invention; Figures 2a, 2b and 2c show alternative coupling structures according to the invention; Figure 3 shows an alternative function of the micro-mechanical clutch according to the invention.

Detailed presentation of invention

With reference to above figures Ia₃ Ib and Ic in the following the structure of the micro-mechanical clutch and of the component integrated with it is described. Figure Ia shows the schematic crosscut of the micro-mechanical clutch in dead state and figure Ib shows the schematic crosscut of the micro-mechanical clutch in active state. Figure Ic shows the clutch schematically from above. In figures Ia, Ib and Ic common reference numbering is used. The dimensions of structures shown in figures Ia, Ib and Ic are presented so that the invention can be advantageously visualized and thus the dimensions do not correspond to the actual dimensions of the clutch according to the invention. As production material of the micro-mechanical clutch silicon wafer is advantageously used, which comprises substrate 100, oxide coating 102, etched part 103, from which the oxide is removed, and topmost a thin silicon layer, i.e. so called SOI layer 104. As surface conduction metal conductors 105 are used and as support 106 of the moving part of the structure insulating material is advantageously used. The thickness of substrate 100 is advantageously of class 50 - 500 μm, the thickness of oxide coating 102 25 - 200 nm and the thickness of SOI layer 104 about 30 -200 mm, which corresponds essentially to structures usually used in microcircuits. The thickness of surface conductor 105 is advantageously 1 - 10 μm and the thickness of supports 106 5 - 50 nm. The micro- mechanical clutch and component 110 integrated with it according to the invention are placed at least partly overlapping on same semiconductor layer together with SOI microcircuits. The dimensions of the clutch determine the area of structure. The dimensions of the clutch can be of a largeness from tens of micrometers to a largeness of millimetres depending on the application area, frequency and operation voltage.

As material of SOI-layer 104 intrinsic semiconductor is used, advantageously unalloyed single crystal silicon. As material of SOI-layer also silicon geranium (Si_xGe₅,) can for instance be used or some other thin film semiconductor, whereby the micro-mechanical clutch is more easily integrated as part of the production of known microcircuits. Since as SOI-layer 104 material other semiconductors than silicon can be used, the term SOI can be extended to mean "Semiconductor-On- Insulator". The thickness of oxide coating 102 correlates exponentially in regard to the voltage level needed for the use of components, so in order to minimize the voltage level the oxide coating must be advantageously as thin as possible. The supports of the micro- mechanical clutch also correlate exponentially in regard to the voltage level needed for the use of the integrated component, so that the supports must advantageously be as thin as possible. Thus a low voltage micro-mechanical clutch is advantageously achieved, as the operating voltage of which typical operating voltage of a microcircuit can be used and with which the integrated component functions advantageously on the operating area of a low impedance. Substrate 100 is advantageously so alloyed at electrodes 105 that its conductivity is essentially high, typically of class 0,1 (Ωcm)^'1 , whereby time constant RC that damps the response of input voltage of the micro-mechanical clutch remains advantageously small. Conductors 105 made on the SOI-layer can be left out, whereby the alloyed areas of the SOI-layer function as conductors and between conductors and SOI-layer non-conductive areas can be made.

Viewed from above the SOI-layer 104 of the micro-mechanical clutch can, in mechanical sense, be divided into two areas: a mechanically moving area 112 and an immobile area 114 surrounding it. Motion is possible, because in the stage of production from the underside of the single crystal silicon layer the oxide coating is etched off so that the silicon film is a self bearing film. There is between the mobile and immobile area an interface 116 fitting said areas mechanically to one another. For control of the micro- mechanical clutch, Le. for voltage supply, an area 105 is formed, which is either an area metallized on the silicon film surface or an area strongly alloyed in the silicon film. Component 110 integrated with the micro-mechanical clutch is at least partly on the moving area of the clutch and advantageously in the centre, where the distance of SOI- layer from the substrate is smallest. Component 110 can be any active or passive electronic component, which can be alloyed in the silicon film or built on it or it can be separately made and joined to the clutch. Advantageously the component is an micro- electro-mechanical component, as for instance a resonator, the impedance level of which can thanks to the high capacitance be made small-sized using typical operating voltage of the microcircuit. The substantial advantage of the micro-mechanical clutch is that with a large clutch structure it is possible, thanks to above presented integration, to achieve for the components a locally high capacitance .With this a technical benefit is achieved so that the voltage amplitude needed for the microcircuit falls essentially. Another important benefit is in the production technology, where there is no need to aim directly at an oxide layer as thin as possible but one can be satisfied with a cheaper and to its availability a better and thicker oxide layer. Then, it is locally possible to achieve by means of he micro-mechanical clutch a very thin distance and thus a high capacitance to the area of the component integrated with the clutch. The properties of the micro-mechanical clutch according to the invention are to their essential part on the other hand influenced by the thickness of the SOI-layer, on the other hand by the surface area of clutch area 112, on the other hand by the thickness of oxide coating 106 and on the other hand by the thickness of oxide coating 102. Since according to an advantageous embodiment of the invention the micro-mechanical clutch can be made in the same semi-conductor layer together with another microcircuit, and since the thickness of SOI-layer and thickness of oxide coating influence the function of other microcircuit, mainly the aim is to influence the surface area of clutch by regulation the thickness of the supports.

The function of the micro-mechanical clutch is based advantageously on the fact that direct voltage (DC-voltage) is conducted to electrode 105. The magnitude of usable voltage can typically be +/-0,5 - 100 magnitude. Mostly the clutch is dead in position Ia and with the voltage coupled in position Ib. Power Fac_tuato_r, directed on active clutch and caused by the film bend depending on DC-voltage is calculated according to formula 1

p ac^"tuator -I _ F ' V £ a„i.r_ — ^A — ₇ • ( ^v1O ' X- where

V = DC-voltage εair = dielectric constant of air, which comprises εo'.n (vacuum permittivity)

A = film surface

X = distance from substrat Harmonic power on its part describes the power, by means of which the aim is to pull back the film towards balance position. Therefore the harmonic power is marked with minus sign. The harmonic power can be calculated according formula 2.

Fspring = -kd (2.) where k = spring constant d = bent distance of film from balance position

The absolute values of power and harmonic power, caused by DC-voltage directed on the micro-mechanical clutch are in a certain point of equal size. When the film is bent more, and when the size of the film path, i.e. the peak-to-peak value is about 1/3 of the oxide coating, then the absolute value of power, caused by the DC-voltage directed on the film of the clutch, is greater than the springback factor. This point is a so called pull-in point, whereby the substrate pulls the film strongly towards itself. The supports under the micro-mechanical clutch receive the film and stops it in this position for as long as the DC-voltage exists. When the DC- voltage is removed the film of clutch returns thanks to the springback factor to its initial position.

Figures 2a, 2b, 2c and 2d the present advantageous embodiments of the micro-mechanical clutch. The dimensions of presented structures are illustrated so that the invention can be easily illustrated, therefore the dimensions do not correspond to the real dimensions of the clutch according to the invention.

Figures 2a, 2b present the micro-mechanical clutch schematically as a crosscut and by them attention is paid to the points, where the structures shown in the figures deviate from the structure presented in figure 1 a.

According to an advantageous embodiment of the invention the clutch can be made for instance according to figure 2a so that clutch supports 210 are fixed to the moving silicon film. According to another advantageous embodiment of the invention the clutch can be made so that the clutch supports 220 are made both in the silicon film and in the substrate. The supports of the micro-mechanical clutch can be made by many different micro-mechanical manufacturing methods either in connection with the manufacture of the SOI wafer or forming the ready-made wafer. The embodiments of the micro-mechanical clutch are not depending on physical forms, or the number of supports but can vary depending on production techniques and applications. Oof supports, or the number of supports, but they can change depending on the realization techniques and on applications. The position of supports can freely vary between the electrodes of clutch and can be done either close or far from the clutch maximum amplitude or they can be done in any of the both electrodes. The clutch according to the invention can be produced also without supports, if the structure of support is fixed to the electrode, towards which the moving part of the clutch is bending.

Figure 2c shows the micro-mechanical clutch schematically viewed from above, and in it attention shall be paid to the place where, where the structure illustrated by the figure deviates from the structure shown in Ic. The micro-mechanical clutch presented in figure 1 can, for instance, also be made in beam form, whereby the silicon film is supported from its two edges and for the two other edges a gap 230 is formed. In the structure of figure 2c it is shown that the embodiments of the micro-mechanical clutch according to the invention are not depending on the geometry of the clutch, but the embodiment can be of any geometric form.

Figure 2d shows the micro-mechanical clutch schematically viewed from above, and in it attention shall paid to the place, where the structure shown by the figure deviates from the structure shown in figure 2c. Figure 2d shows the micro-mechanical clutch according to the invention, the motion of which is in level xy direction and at the same time the figure shows both the normal state and the extreme position of motion. Here is pointed out that the direction of the carried out motion can be any xyz direction of three-dimensional space or some combination of these basic directions. Advantageously the direction of clutch motion is one of the main xyz directions and can change within the frames of the claims. Figure 3 shows the micro-mechanical clutch schematically as a crosscut and in it attention hall be paid to the function of the invention as a connectable clutch. The micro-mechanical clutch can also be used in couplings, where onto the clutch another as for instance, by means of ball or papillary bonding 320. Then, for instance, the micro- mechanical clutch according to the invention can function so that the clutch is by means of DC-voltage bent towards microcircuit 310 as shown in figure 3. In this case the micro- mechanical clutch works as joining element, and the component integrated with it can, for instance, be a conductor by means of which a signal is taken from SOI-circuit to the circuit joined to it.

The clutch structures according to the invention are especially usable in different wireless communication equipment, as for instance GMS- and UMTS-mobile stations and in broadband networks of the 4. generation. Other useful systems are, among others, Bluetooth, WLAN IEEE 802.11 FflPERLAN (High Performance Radio Local Area Network). In these systems the main equipment uses frequencies that change about between 900MHz - 5,8 GHz. For professionals in the field it is obvious that when the technique advances the basic concept of the invention can be achieved in many ways. The invention and its embodiments do thus not be restricted to the above examples but can change within the frames of the claims.

Claims

1. A micro-mechanical clutch formed of a clutch formed on the surface of a semiconductor film (100) and comprising a level (104) moving in regard to film(lOO), characterized in that said level (104) is mechanically moving in steps and including an electronic component (110) placed at least partly overlapping it, and the said moving level is fitted to move as response to direct voltage fed into level (104).

2. A clutch according to claim 1 characterized in that the surface area of level (104) essentially comprises a mechanically, in steps moving level portion, (112) and an immobile portion (114), whereat the surface area of level (112) comprises a first area, which comprises area (105) that causes the mechanical motion, and a second area that comprises an electronic component (110).

3. A clutch according to claim 1 characterized in that the current of said component (110) changes as response to the position of the mechanically, in steps moving level (110).

4. A clutch according to claim 2 characterized in that said area (105) causing mechanical vibration is of alloyed semiconductor or coated with a conductor layer.

5. A clutch according to claim 1 or 2 characterized in that the area of moving level (104) comprises at least one electrically insulating or partly insulating mechanical support. (106).

6. A clutch according to any above claim characterized in that the dead moving level (104) forms the first operating point, in which point the level is in off- position and the moving active level (104) forms the second operating point, in which point level (104) rests on mechanical supports (106).

7. A clutch according to any above claim 1-6 characterized in that component (110) is made in the SOI-structure, which comprises the substrate, an insulating oxide coating and topmost a semiconductor layer, onto which said micro- mechanical clutch, including the conductor layer on it, is formed.

8. A clutch according to claim 7 characterized in that the said semiconductor layer is of unalloyed single crystal silicon, silicon germanium or some other material used in thin film microcircuits.

9. A clutch according to claim 8 characterized in that the said semiconductor layer is as to thickness essentially 50 - 200 nm, advantageously 70 - 100 nm.