JP2008030182A - Constant amplitude mechanism and electric potential sensor with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a MEMS device using the vibration amplitude of a micro-structure, which has resistance to environmental or secular changes. <P>SOLUTION: This MEMS device is provided with the micro-structure with a movable electrode array 102 for measuring capacitance between an object and itself, a micro-actuator composed of piezoelectric micro-cantilevers 108a, 108b using piezoelectric elements for vibrating the micro-structure, a connection section composed of hinges 112a, 112b connecting the micro-structure and the micro-actuator in a freely oscillating manner, and stoppers 110a, 110b contacting with the micro-structure and controlling the amplitude thereof when it is vibrated by the micro-actuator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to MEMS (Micro Electro Mechanical Systems), and is particularly suitably applied to a MEMS device in which a microstructure is driven by a microactuator that uses electrostatic, electromagnetic, heat, piezoelectric, or the like as a driving source. sell.

  MEMS devices often have a structure in which a microstructure is driven by a microactuator using electrostatic, electromagnetic, heat, piezoelectric, or the like as a drive source. As a driving method, there are a static drive driven by a direct current, a quasi-static drive driven by an alternating current of a non-resonant frequency, and a resonant drive driven by an alternating current of a resonant frequency.

  Among these, in the case of resonance driving, the vibration amplitude of the microstructure may change due to the change of the resonance frequency accompanying the environmental change such as temperature. In addition, with the long-term use of the MEMS device, the characteristics of the microactuator and the microstructure may change, resulting in an amplitude change.

  For this reason, in a conventional MEMS device, particularly a MEMS device that needs to vibrate a microstructure with a constant amplitude, the amplitude is detected by a sensor or the like, the detection signal is amplified by an amplifier, and feedback by a signal processing circuit is applied. Loop control is performed.

  However, when such a method is adopted, a plurality of elements other than the MEMS device main body such as a detection sensor, an amplifier, and a signal processing circuit are necessary in hardware, and amplitude detection → amplification → A multi-step process of determination → feedback is required.

Texas Instruments, Inc. has a projection technology called DLP (registered trademark) in which a large number of micromirrors manufactured by applying MEMS technology are arranged. The angles of the individual micromirrors constituting the DLP projector can be changed, and an image is projected by variably controlling the angles of several hundred thousand micromirrors. In order to regulate the tilt of the DLP micromirror, a stopper for regulating the tilt is provided at the lower part of the mirror (see Non-Patent Document 1 FIG. 4). However, although the angle of the DLP micromirror is variably controlled, it is not vibrated, and the tilt is restricted, but the vertical movement is not restricted. Furthermore, DLP micromirrors are not used as sensors to measure the properties of objects.
Larry J. Hornbeck's "Digital Light Processing and MEMS: Timely Convergence for a BrightFuture" (Texas Instruments, Inc.) is unknown. Obtain from: http://www.dlp.com/dlp_technology/images/dynamic/white_papers/115_Digital_Light_Processing_MEMS_Timely_Convergence.pdf

  The present invention is to solve one or more of the problems described above, and in a MEMS device including a structure that can be vibrated by a microactuator, the amplitude of the structure is regulated by a stopper. Is one of its features.

  According to the present invention, since the maximum amplitude at which the structure can vibrate is physically defined by the stopper, the vibration characteristics of the structure itself change due to a change in the resonant frequency accompanying an environmental change such as temperature, The vibration amplitude can be kept constant even if it changes due to the change in the characteristics of the actuator or the structure with the long-term use. In addition, all that is necessary to control the vibration amplitude is to drive the structure near the resonance frequency in the environment, which eliminates the need for amplitude detection, amplification, determination, and feedback. Thus, the control circuit can be overwhelmingly simplified.

  In order to keep the amplitude of the structure constant over a long period of time with respect to the aging of the device, the amplitude of the structure defined by the stopper can be caused to vibrate the structure by the actuator at the beginning of manufacturing the device. It is preferable to set it smaller than the maximum amplitude.

  Such a MEMS device can be suitably applied to, for example, a sensor that measures the property of an object using the vibration characteristics of the device. That is, the sensor using the MEMS device according to the present invention has a high ability to keep the vibration amplitude constant with respect to environmental changes and secular changes, so that stable measurement is possible and a control circuit compared to the conventional one. Since the sensor can be greatly simplified, there are cases where the sensor can be reduced in size and simplified as compared with the conventional case, and there is a possibility that it can contribute to the cost reduction of the sensor.

  While examples of preferred embodiments of the present invention are set forth in the appended claims, the present invention covers all features and combinations thereof that are explicitly and implicitly described in this specification and the accompanying drawings. Are also included within the scope.

  One of the preferred embodiments of the present invention is a MEMS device, which is a microstructure, a microactuator for causing the microstructure to vibrate, and swinging the microstructure and the microactuator. A MEMS device comprising: a coupling portion that freely couples; and a stopper that contacts the microstructure and regulates the amplitude of the microstructure when the microstructure is vibrated by the microactuator.

  MEMS is an abbreviation for a microelectromechanical system, but typical dimensions of a MEMS device according to a preferred embodiment of the present invention include a surface size of 100 μm × 100 μm to 10 mm × 10 mm, and a thickness of 1 μm. It is about 20 μm. Of course, this does not mean that all the MEMS devices according to the present invention are limited to this size.

  In the above MEMS device, the microactuator can be driven by electrostatic, electromagnetic, thermal, piezoelectric, or the like. Moreover, it is preferable that the amplitude of the microstructure defined by the stopper is set smaller than the maximum amplitude at which the microactuator can vibrate the microstructure at the beginning of manufacturing the MEMS device.

  In a more specific embodiment of the MEMS device according to the above embodiment, the microstructure is configured such that a thin plate-like flap is provided at an end thereof, and the stopper is disposed so as to sandwich the flap. When the microstructure is vibrated by the microactuator, the flap portion interferes with the stopper, so that the amplitude of the microstructure can be reduced. Can be configured to be regulated. By adopting a stopper structure that sandwiches the flap portion provided at the end of the microstructure, the amplitude of the microstructure can be easily defined in the direction in which the stopper is sandwiched.

  Furthermore, in the above-described embodiment, the microstructure may have a thin rectangular parallelepiped shape, and the flap and the stopper may be provided on both sides of the long side of the microstructure. Furthermore, you may comprise so that the two said micro actuators may be connected with the both sides of the short side of the said micro structure through the said connection part, respectively.

  Further, in the above-described embodiment, the interval between the two plate-like structures is larger than the maximum amplitude at which the microactuator can vibrate the microstructure when the MEMS device is initially manufactured without the stopper. Alternatively, it may be configured to be small.

  One of the preferred embodiments of the present invention is a sensor including the MEMS device according to the present invention, wherein the micro structure includes an electrode, and the micro actuator causes the micro structure to swing. A sensor having a measuring device for measuring a change in the amount of charge accumulated in the electrode caused by The sensor may be configured such that a plurality of electrodes connected to the measuring device are arranged in the microstructure.

  FIG. 1 is a diagram schematically showing a MEMS potential sensor 100 as an example of a preferred embodiment of the present invention. 1A is a view of the sensor 100 as viewed from above, FIG. 1B is a cross-sectional view taken along line YY shown in FIG. 1A, and FIG. 1C is FIG. It is sectional drawing of the XX line shown by this. The MEMS potential sensor 100 has a plurality of electrodes 104 on its upper surface and a movable electrode array 102 having flaps 106a and 106b on both sides thereof, piezoelectric micro-cantilevers 108a and 108b for driving the movable electrode array 102, and a flap 106a. , 106b and two stoppers 110a, 110b each having a plate-like structure. The movable electrode array 102 and the piezoelectric micro-cantilevers 108a and 108b are connected by hinges 112a and 112b that connect the movable microarray cantilevers 108a and 108b in a swingable manner.

  The piezoelectric micro cantilevers 108a and 108b are composed of a metal material, a piezoelectric material, and a structural material. Examples of metal materials that can be used include Pt, Au, Ti, Cr, Ni, and Ag. Examples of piezoelectric materials include lead zirconate titanate, zinc oxide, and aluminum nitride. Examples of the structural material include silicon, silicon oxide film, silicon nitride film, alumina, and glass. The movable electrode array 102 is configured using the above structural material and a metal that can be used as an electrode. The stoppers 110a and 110b and the hinges 112a and 112b can also be configured using the same structural material.

  Although it is only an example, the size of the MEMS potential sensor 100 actually created in the research and development of the present invention is listed for reference. The movable electrode array 102 had a length of 4 mm including the flaps 106 a and 106 b and a width of 0.5 mm. The size of the overlap between the flaps 106a and 106b and the stoppers 110a and 110b was 0.5 mm × 0.5 mm. The piezoelectric micro cantilevers 108a and 108b were squares having a length and a width of 2 mm. The stoppers 110a and 110b had a trapezoidal shape as depicted in FIG. 1a, and had an upper side length of 1.5 mm and a bottom side length of 3 mm. Various distances between the two plate-like structures in the stoppers 110a and 110b were created in the range from 1 μm to 100 μm.

  Next, the principle of operation of the MEMS potential sensor 100 will be described with reference to FIGS. 1 and 2. When a periodically varying voltage is applied to the piezoelectric micro cantilevers 108a and 108b, they vibrate due to the piezoelectric effect. This vibration is transmitted to the movable electrode array 102 via the hinges 112a and 112b, and causes the movable electrode array 102 to vibrate up and down (see FIG. 1b). Since the piezoelectric micro cantilevers are provided on both sides on the short side of the movable electrode array 102, the movable electrode array 102 can be vibrated more stably than when only one piezoelectric micro cantilever is used. When the voltage applied to the piezoelectric micro cantilevers 108a and 108b is adjusted so that the vibration frequency of the movable electrode array 102 becomes the resonance frequency of the movable electrode array 102, the amplitude of the movable electrode array 102 can be maximized. Here, when the object to be measured 200 is placed on the movable electrode array 102, the distance D between the object 200 to be measured and the movable electrode array 102 changes dynamically due to the vibration of the movable electrode array 102, thereby The capacitance C between the two changes, and further, the charge Q accumulated in the electrode 104 changes. By measuring the change in the charge Q and using the capacitor equation Q = CV, the potential of the DUT 200 can be obtained.

  As can be understood from the above description, in order to accurately reflect the change in the charge Q to the potential of the device under test 200, the capacitance C must be obtained accurately. The change in the distance D between the object 200 and the movable electrode array 102 must be accurately grasped. Therefore, it is understood that it is very important to keep the amplitude d of the movable electrode array 102 constant. However, according to the prior art, the amplitude of the movable electrode array 102 has changed over time due to environmental changes such as temperature and aging of the sensor 100 itself. In order to perform accurate potential measurement in consideration of the change, it is necessary to provide a detection sensor and a determination circuit for measuring the amplitude of the movable electrode array separately, and to apply feedback according to the result of the determination circuit. .

  However, in the potential sensor 100, since the flaps 106a and 106b provided on both sides of the movable electrode array 102 interfere with the stoppers 110a and 110b and the operation of the potential sensor 100 is restricted, the amplitude of the movable electrode array 102 is different from that of each stopper. It is defined by the size of the interval between two opposing plate-like structures. Accordingly, the potential sensor 100 has a very high ability to keep the amplitude of the movable electrode array 102 constant against environmental changes and aging, and has a stable voltage measurement ability over a long period of time compared to a conventional sensor of the same type. Can keep.

  In order to keep the amplitude of the movable electrode array 102 constant over a long period of time, the distance between the two plate-like structures in the stoppers 110a and 110b is set to be larger than the maximum amplitude of the movable electrode array 102 at the beginning of manufacturing the MEMS potential sensor 100. It is preferable to set it to be small. FIG. 3 is a diagram showing the result of a simulation in which how the amplitude of the movable electrode array 102 changes due to environmental changes and secular changes. Compared to the initial state 301, the resonance frequency shift is observed in the simulation result (302) considering the environmental change, and the simulation result (303) considering the fatigue of the piezoelectric microcantilever accompanying long-term use is the movable electrode. It can be seen that the maximum amplitude of the array 102 is much smaller than the initial state (301). However, in the stoppers 110a and 110b, the distance between the two opposing plate-like structures of each stopper is set as shown in (304) of FIG. 3, and the amplitude of the movable electrode array 102 is shown in (304). By defining the size of the movable electrode array 102, the amplitude of the movable electrode array 102 can be kept constant regardless of environmental changes and secular changes. By appropriately determining the distance between the stoppers, the amplitude of the movable electrode array 102 can be kept constant even if the maximum amplitude is reduced to half or less of the initial state.

  Further, it should be noted that the control for keeping the amplitude of the movable electrode array 102 constant is only driven near the resonance frequency in the normal environment, so that the amplitude detection, amplification, No determination, feedback, or the like is required, and the control circuit can be overwhelmingly simplified. FIG. 4 summarizes the advantages of the present invention over the prior art.

  Finally, an example of a method for manufacturing the MEMS potential sensor 100 will be briefly described with reference to FIG. First, a structure in which the movable electrode array 102 and the micro cantilevers 108a and 108b are connected by hinges 112a and 112b is manufactured using a known MEMS microfabrication technique, and this is sandwiched between an upper stopper wafer and a lower stopper wafer. The stopper structure is formed by bonding at the above. Each of the stopper wafers is etched so that the gap when finally sandwiched becomes the target value d. If d is 1 mm or more, it can be realized by a standard silicon dry etching technique.

  Next, the produced stopper wafers are bonded together while being aligned. In bonding, a method can be adopted in which holes are provided outside the respective wafers, and the wafers are aligned by passing guide pins through the holes. Like the MEMS potential sensor 100 described above, the size of the area where the stopper interferes with the flap is designed with a margin such as 0.5 mm × 0.5 mm, so that a desired position can be obtained without precise positioning. A stopper structure can be easily formed. For the bonding, anodic bonding, bonding using an adhesive, bonding using a eutectic reaction between gold and silicon previously formed on a bonding surface, or the like is used.

  The embodiments of the present invention have been described above by way of examples. However, the above-described embodiments are not intended to limit the present invention, and the present invention can take various embodiments without departing from the scope of the present invention. It goes without saying that it is possible. The present invention includes in its scope any combination of the various features exemplified herein.

It is the figure on which the outline of the MEMS electric potential sensor 100 which is one Embodiment of this invention was drawn. 3 is a diagram for explaining an operation principle of the MEMS potential sensor 100. FIG. It is a figure which shows the investigation result of the influence of the environmental change and secular change of the movable electrode array used for the MEMS potential sensor. It is the figure which summarized the advantage of this invention compared with a prior art. 6 is a diagram for explaining an example of a method for manufacturing the MEMS potential sensor 100. FIG.

Explanation of symbols

100 MEMS potential sensor 102 movable electrode array 104 electrodes 106a and 106b flaps 108a and 108b piezoelectric micro cantilevers 110a and 110b stoppers 112a and 112b hinges

Claims (8)

A microstructure,
A microactuator for causing the microstructure to vibrate;
A connecting portion for oscillatingly connecting the microstructure and the microactuator;
When the microstructure is vibrated by the microactuator, a stopper that contacts the microstructure and restricts the amplitude of the microstructure,
A MEMS device comprising:   The amplitude of the microstructure defined by the stopper is set to be smaller than a maximum amplitude at which the microactuator can vibrate the microstructure at the beginning of manufacturing the MEMS device. MEMS devices. The microstructure is provided with a thin plate-like flap at its end,
The stopper has two plate-like structures disposed so as to sandwich the flap,
When the microstructure is vibrated by the microactuator, the flap portion interferes with the stopper so that the amplitude of the microstructure is regulated.
The MEMS device according to claim 1 or 2.   The MEMS device according to claim 3, wherein the microstructure has a thin rectangular parallelepiped shape, and the flap and the stopper are provided on both sides of the long side of the microstructure.   5. The micro structure according to claim 3, wherein the micro structure has a thin rectangular parallelepiped shape, and the two micro actuators are coupled to both sides of the short side of the micro structure via the coupling portion, respectively. MEMS device.   The interval between the two plate-like structures is set to be smaller than the maximum amplitude at which the microactuator can vibrate the microstructures when the MEMS device is initially manufactured without the stopper. The MEMS device according to any one of claims 3 to 5.   A sensor comprising the MEMS device according to claim 1, wherein the sensor measures a property of an object using vibration characteristics of the microstructure. A sensor comprising the MEMS device according to claim 1, wherein the microstructure is provided with an electrode, and the microactuator is accumulated on the electrode generated by vibrating the microstructure. A sensor comprising a measuring device for measuring a change in the amount of charge.