JP2009139173A - Device and method for measuring capacity variation of microstructure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a capacity variation measuring device and a capacity variation measuring method of a microstructure for measuring microvolume with a simple measuring circuit. <P>SOLUTION: The microstructure 1 comprises a fixed section electrode 4 and a movable section electrode 5 that is arranged facing to the fixed section electrode 4 and has a capacitance between it and the fixed section electrode 4. A bias generation circuit 20 applies a bias potential between the fixed section electrode 4 and the movable section electrode 5. A current measurement circuit 30 detects the current flowing between the fixed section electrode 4 and the movable section electrode 5 when the bias potential is applied. A current variation detection discrimination circuit 40, based on the detected variation in current with time, measures the variation in capacitance between the fixed section electrode 4 and the movable section electrode 5. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a capacitance change measuring apparatus and a capacitance change measuring method for a microstructure that measures changes in capacitance between electrodes of the microstructure such as an acceleration sensor and an angular velocity sensor.

  In recent years, for example, multi-axis acceleration sensors and multi-axis angle sensors using a micro electro mechanical system (MEMS) have been widely used as microstructure devices in many fields such as acceleration sensors for automobile airbags. In order to confirm the operation of such a microstructure, a change in capacitance between the fixed electrode and the movable electrode is measured.

For example, Japanese Patent Laid-Open No. 2000-55956 (Patent Document 1) describes a system for measuring a minute capacity. In the measurement of a minute capacitance according to Patent Document 1, a prober is brought into contact with a measurement electrode, and the capacitance is measured by a capacitance measuring device.
JP 2000-55956 A

  In the capacitance measuring method in which a prober is brought into contact with a measurement electrode as described in Patent Document 1, there is a problem that the prober is easily affected by the cable length of the prober and parasitic capacitance. In addition, in the microstructure, the capacitance between the fixed electrode and the movable electrode changes at a high speed, so it is difficult to shorten the measurement time when a measurement system using a prober is applied to the measurement of a minute capacitance. There is also a problem.

  Accordingly, an object of the present invention is to provide a capacitance change measuring device and a capacitance change measuring method for a microstructure capable of measuring a minute capacitance with a simple measurement circuit as compared with capacitance measurement.

  The present invention relates to a capacitance change measuring device for a microstructure having a fixed part electrode and a movable part electrode disposed opposite to the fixed part electrode and having a capacitance between the fixed part electrode and the fixed part electrode. A voltage applying means for applying a voltage between the partial electrode and the movable part electrode, and a current detecting means for detecting a current flowing between the fixed part electrode and the movable part electrode when a voltage is applied by the voltage applying means; And detecting means for detecting a change in capacitance between the fixed part electrode and the movable part electrode based on the time change of the current detected by the current detecting means.

  In the present invention, since the change in capacitance can be detected based on the change in the current waveform, it is not affected by the cable length or parasitic capacitance compared to the case where the capacitance is detected by a probe or the like.

  Preferably, the capacitance change detecting means stores a measured value within a predetermined range corresponding to the capacitance during normal operation of the microstructure, and the measured value range stored by the measured value at the time of measurement is stored. It is detected whether or not the microstructure operates normally depending on whether or not it is inside.

  By comparing the measured value within the range stored in advance with the measured value of the microstructure, it can be determined whether or not the microstructure operates normally.

  Preferably, the memorized measurement value within the predetermined range is the difference in the amount of deformation of the waveform with respect to the current waveform, the difference in the amount of distortion, the voltage difference with respect to the peak value of the current waveform, the current during the normal operation of the microstructure. One of the phase differences with respect to the waveform.

  It can be determined whether the microstructure is operating normally from any of these measured values.

  Preferably, the voltage applying means applies an AC voltage whose level changes with time between the fixed part electrode and the movable part electrode.

  As an AC voltage, a sine wave, a triangular wave, a sawtooth wave, or the like can be used.

  Another aspect of the present invention is a capacitance change measuring method for a microstructure including a fixed part electrode and a movable part electrode disposed opposite to the fixed part electrode and having a capacitance between the fixed part electrode. A step of applying a voltage between the fixed portion electrode and the movable portion electrode, a step of detecting a current flowing between the fixed portion electrode and the movable portion electrode when the voltage is applied, and And detecting a change in capacitance between the fixed part electrode and the movable part electrode based on the time change of the current.

  Also according to the method of the present invention, since the change in capacitance can be detected based on the change in the current waveform, it is not affected by the cable length or parasitic capacitance compared to the case where the capacitance is detected by a probe or the like. .

  Preferably, based on whether or not the detected change in capacitance is within the measurement value of the microstructure stored in advance during normal operation, whether the microstructure being measured operates normally Judge whether.

  Also in this example, it can be determined whether or not the microstructure operates normally.

  A voltage is applied between the fixed part electrode and the movable part electrode, and when a voltage is applied, a current flowing between the fixed part electrode and the movable part electrode is detected, and a minute amount is determined based on the detected change in the current. Since the change in the capacitance of the structure is measured, it is not affected by the cable length or parasitic capacitance, and it is possible to measure a minute capacitance with a simple configuration, thereby facilitating operation detection.

  FIG. 1 is a block diagram showing an apparatus for measuring a change in capacitance of a microstructure in one embodiment of the present invention, and FIG. 2 is a waveform diagram showing changes in bias potential and capacitance. In FIG. 1, a microstructure 1 is, for example, an acceleration sensor that detects acceleration when a speed is applied from the outside. The microstructure 1 includes a fixed part electrode 4 including a first electrode 2 and a second electrode 3, and a movable part electrode 5 disposed to face the fixed part electrode 4. The microstructure 1 is arranged so that the movable part electrode 5 and the fixed part electrode 4 are horizontal, and the movable part electrode 5 resonates when acceleration or vibration is applied. A resonance signal is extracted as a detection signal from between the second electrode 3 and the movable part electrode 5 of the fixed part electrode 4.

  A bias potential a based on a sine wave bias signal shown in FIG. 2A is supplied from a bias generation circuit 20 that operates as a voltage application unit, via a current measurement circuit 30 that operates as a current detection unit, for operation confirmation. It is applied between the first electrode 2 and the movable part electrode 5 of the microstructure 1. The movable part electrode 5 is displaced according to the bias potential, and the capacitance change b of the electrostatic capacity shown in FIG. 2B according to the displacement is detected as the second electrode 3 of the fixed part electrode 4 and the movable part electrode. 5 and a detection signal is given to the detection circuit 50. The detection circuit 50 converts the change in capacitance into a change in voltage signal, and outputs a voltage signal corresponding to the change in capacitance between the second electrode 3 of the fixed part electrode 4 and the movable part electrode 5.

  The current measurement circuit 30 measures the current flowing between the first electrode 2 and the movable part electrode 5 when a bias signal is applied between the first electrode 2 and the movable part electrode 5 from the bias generation circuit 20. To do. The measured current measurement signal is given to a current change detection discriminating circuit 40 that operates as a capacity change detecting means. The current change detection discriminating circuit 40 includes frequency analysis by FFT (Fast Fourie Transform), distortion rate measurement by a distortion meter, and the like.

  3A and 3B are diagrams showing the structure of the microstructure 1 shown in FIG. 1, FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. . An oxide insulating film 11 is formed over the substrate 10 illustrated in FIG. 3B, and the microstructure 1 is formed over the oxide insulating film 11.

  That is, the movable part electrode 5 shown in FIG. 1 is in one direction orthogonal to the longitudinal direction of the weight part 51 of the movable part electrode to which the comb-like electrode is connected in FIG. 3 and the weight part 51 of the movable part electrode. A plurality of movable part comb-like electrodes 52 extending in a comb-like shape, a plurality of movable part comb-like electrodes 53 extending in the other direction, and movable part springs 54 and 55 for supporting both ends of the weight part 51 of the movable part electrode. And anchor portions 56 and 57 for fixing the movable portion springs 54 and 55. The anchor portions 56 and 57 are formed on the oxide insulating film 11. However, the movable portion springs 54 and 55, the weight portion 51 of the movable portion electrode and the plurality of movable portion comb-like electrodes 52 and 53 are formed on the oxide insulating film 11. It is not fixed to, so it will move or displace when velocity is applied.

  The first electrode 2 and the second electrode 3 of the fixed part electrode 4 are provided separately from each other, and are formed on the oxide insulating film 11 so as to sandwich the movable part electrode 5. The first electrode 2 includes a comb-like portion 21 positioned between a plurality of movable-part comb-like electrodes 52 extending from one side of the weight part 51 of the movable-part electrode of the movable-part electrode 5. The second electrode 3 includes a fixed portion comb-like portion 31 positioned between a plurality of movable portion comb-like electrodes 53 extending from the other side of the weight portion 51 of the movable portion electrode 5 of the movable portion electrode 5.

  The interval between the comb-like portion 21 and the movable portion comb-like electrode 52 is arranged such that the upper gap G2 is wide and the lower gap G1 is narrow. Conversely, the interval between the fixed portion comb-like portion 31 and the movable portion comb-like electrode 53 is arranged such that the upper stage is narrow and the lower stage is wide. The capacitance value between the electrodes is larger when the distance between the electrodes is narrower, and the capacitance value changes when the distance between the electrodes is originally narrower when the distance is the same. Therefore, the change in the comb-tooth portion 21, the movable portion comb-tooth electrode 52, and the capacitance value is predominantly affected by the change in the lower inter-electrode distance. On the contrary, the change in the inter-electrode distance in the upper stage is dominantly affected by the change in the capacitance value of the fixed-part comb-teeth part comb-teeth part 31, the movable part comb-teeth electrode 53 and the capacitance value.

  When acceleration is applied to the longitudinal direction of the weight portion 51 of the movable portion electrode, and the weight portion 51 of the movable portion electrode and the movable portion comb-like electrodes 52 and 53 are displaced upward in the drawing by inertial force, the comb-like portion The capacitance value between 21 and the movable portion comb-like electrode 52 increases, and conversely, the capacitance value between the fixed portion comb-like portion 31 and the movable portion comb-like electrode 53 decreases. By monitoring the difference between the two capacitance values, the displacement of the movable part due to the inertial force, that is, the index of acceleration can be monitored. This is the operation of the microstructure 1 as an acceleration sensor.

  A bias application pad 22 is formed at one end of the first electrode 2, a detection electrode pad 32 is formed at one end of the second electrode 3, and a movable part detection pad is provided at the anchor part 57 of the movable part electrode 5. 58 is formed. Probe pads of a probe card (not shown) come into contact with these pads 22, 32, and 58, and a bias signal is applied or a detection signal is taken out.

  The bias output outputted from the bias generation circuit 20 shown in FIG. 1 is connected to the bias application pad 22 and the movable part detection pad 58, and a bias is applied to the comb-like part 21 and the movable part comb-like electrode 52. The The signal input of the detection circuit 50 is connected to the detection electrode pad 32 and the movable part detection pad 58. When a bias signal is applied between the first electrode 2 and the movable part electrode 5, the movable part electrode 5 is displaced, the capacitance between the second electrode 3 and the movable part electrode 5 changes, and the movable part electrode A detection signal corresponding to the displacement of 5 appears.

  FIG. 4 is a waveform diagram showing waveforms of voltage V and current I when the distance between the electrodes does not change when a bias potential is applied. The horizontal axis indicates time t (sec), and the left vertical axis indicates the bias potential. V (V) is shown, and the right vertical axis shows the current I (A).

  FIG. 5 is a waveform diagram showing the waveform of the bias potential V (V) and the force F (N) acting between the first electrode 2 and the movable part electrode 5 due to the Coulomb force, and the horizontal axis represents time t (sec. ), The left vertical axis indicates the bias potential V (V), and the right vertical axis indicates the Coulomb force F (N).

  FIG. 6 is a waveform diagram showing changes in the gap G (d) and the capacitance C (F) between the comb-like portion 21 and the resonant beam 52 due to the movable portion electrode 5 being drawn. Indicates time t (sec), the left vertical axis indicates capacitance C (F), and the right vertical axis indicates gap G (d).

  FIG. 7 is a waveform diagram showing the waveform of the current I (A) flowing when the bias potential V (V) of the sine wave signal is applied and the waveform of the distorted current I2 (A). Indicates time t (sec), and the left vertical axis indicates current I (A).

  Next, with reference to FIGS. 4 to 7, the operation of the capacitance change measuring apparatus 1 for a microstructure in one embodiment of the present invention will be described. For example, when a bias potential of 5 V is applied between the first electrode 2 and the movable part electrode 5 with a sine wave having a frequency of 1 kHz from the bias generation circuit 20 shown in FIG. Since the capacitance between the first electrode 2 and the movable part electrode 5 functions as a capacitor, the waveform of the current I (A) is 90 degrees out of phase with the waveform of the voltage V (V) as shown in FIG. Advancing, the amplitude is constant and the period is 1 kHz.

  At this time, the bias potential V is applied between the first electrode 2 and the movable part electrode 5, whereby a force F (N) acts on the movable part electrode 5 by Coulomb force. This force F (N) is expressed by the following equation. In the following equation, d is the distance between the gaps, and S is the area of the movable part electrode 5.

  As shown in FIG. 5, the change in the bias potential V (V) and the force F (N) due to the Coulomb force change almost following the change in the bias potential V (V). The distance between the gaps changes in accordance with the force F (N) due to. When the frequency f of the bias potential V (V) coincides with the resonance frequency of the movable part electrode 5 of the microstructure 1, the displacement amount of the movable part electrode 5 increases, so that the distance between the first electrode 2 and the movable part electrode 5 is increased. However, this is an attendant effect.

  When a force F (N) is applied to the movable part electrode 5, the movable part electrode 5 is displaced based on a constant spring constant by the movable part springs 54 and 55, so that the comb-like shape of the first electrode 2 shown in FIG. The gaps G1 and G2 between the portion 21 and the movable portion comb-like electrode 52 of the movable portion electrode 5 change. If the spring constants of the movable part springs 54 and 55 are large, the rise and fall of the gap G shown in FIG. Changes in the gap G (d) and the capacitance C (F) due to the movable part comb-like electrode 52 of the movable part electrode 5 being attracted to the comb-like part 21 of the first electrode 2 are expressed by the following equations.

  Further, as shown in FIG. 6, the capacitance C (F) and the gap G (d) change with time. As shown in FIG. 6, the capacitance C (F) is increased when the gap G (d) is small, and the capacitance C (F) is decreased when the gap G (d) is large.

  When the capacitance C (F) changes with the change of the bias potential V (V), as shown in FIG. 7, the current I2 (A) is distorted. The current I (A) shown in FIG. This is a current waveform that flows when V (V) is a sine wave.

  The current measurement circuit 30 shown in FIG. 1 measures the current I2 (A) that causes the distortion shown in FIG. 7, and the current change detection determination circuit 40 determines that the microstructure 1 has a bias potential based on the measured current. That is, it is determined whether or not the coulomb force is changed based on a predetermined spring constant by the movable part springs 54 and 55. For example, frequency analysis by FFT and distortion rate measurement by a distortion rate meter can be applied to the detection and discrimination of changes in the current waveform.

  The current change detection discriminating circuit 40 corresponds to a capacitance value within a range in which the microstructure 1 that normally operates normally can be determined to be normal, a difference in waveform deformation amount relative to a current waveform, a difference in distortion amount, a current Whether the voltage difference with respect to the peak value of the waveform or the phase difference with respect to the current waveform is stored, and whether the measured value of the microstructure 1 to be inspected at the time of inspection is within the range of stored values By determining whether or not, it is possible to determine whether or not the microstructure 1 to be inspected is normal.

  When a DC voltage or a rectangular wave is applied between the first electrode 2 and the movable part electrode 5 as the bias potential V (V), the first electrode 2 and the movable part of the microstructure 1 are applied when the DC voltage is applied. While a charge is charged in the capacitance C (F) formed between the electrodes 5, a current having a constant time constant flows, and in this process, between the first electrode 2 and the movable part electrode 5. When the Coulomb force F (N) is generated and the movable part electrode 5 is displaced, there is a change in the time constant at which the current decreases. It can be detected from this change in the current waveform whether the microstructure is changing based on a predetermined spring constant by the voltage, that is, the Coulomb force F (N).

  As mentioned above, although embodiment of this invention was described with reference to drawings, this invention is not limited to the thing of embodiment shown in figure. Various modifications and variations can be made to the illustrated embodiment within the same range or equivalent range as the present invention.

It is a block diagram which shows the capacitance change measuring apparatus of the microstructure in one Example of this invention. It is a wave form diagram which shows a bias potential and a capacitance change. 2A and 2B are diagrams illustrating the structure of the microstructure shown in FIG. 1, in which FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. It is a wave form diagram which shows the change of the waveform of the voltage V and the electric current I when the distance between electrodes does not change when a bias potential is applied. It is a wave form diagram which shows the change of the waveform of bias electric potential V (V), and force F (N) which acts between the 1st electrode 2 and the movable part electrode 5 by Coulomb force. It is a wave form diagram which shows the change of the gap G (d) and the electrostatic capacitance C (F) between the comb-tooth shaped part 21 and the resonance beam 52 by the movable part electrode 5 being drawn. It is a wave form diagram which shows the waveform of the electric current I (A) which flows when the bias electric potential V (V) of a sine wave signal is applied, and the electric current I2 (A) which produced the distortion.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Micro structure, 2 1st electrode, 3 2nd electrode, 4 Fixed part electrode, 5 Movable part electrode, 10 Substrate, 11 Oxide insulating film, 20 Bias generation circuit, 21, 31 Comb-like part, 22 Bias application pad , 30 Current measurement circuit, 40 Current change detection discrimination circuit, 32 Detection electrode pad, 50 Detection circuit, 51 Weight part of movable part electrode, 52, 53 Movable part comb-like electrode, 54, 55 Movable part spring, 56, 57 Anchor part.

Claims (6)

Capacitance change measurement for measuring a change in capacitance of a microstructure including a fixed portion electrode and a movable portion electrode disposed opposite to the fixed portion electrode and having a capacitance between the fixed portion electrode and the fixed portion electrode. A device,
Voltage applying means for applying a voltage between the fixed part electrode and the movable part electrode;
Current detecting means for detecting a current flowing between the fixed part electrode and the movable part electrode when a voltage is applied by the voltage applying means;
Capacitance of the microstructure including a capacitance change detecting means for detecting a change in capacitance between the fixed part electrode and the movable part electrode based on a time change of the current detected by the current detecting means. Change measuring device.   The capacitance change detecting means stores a measured value within a predetermined range corresponding to the capacitance during normal operation of the microstructure, and the measured value at the time of measurement is the range of the stored measured value The capacitance change measuring device for a microstructure according to claim 1, wherein whether or not the microstructure operates normally is detected depending on whether or not it is inside.   The stored measurement values within the predetermined range are the difference in the amount of deformation of the waveform with respect to the current waveform, the difference in the amount of distortion, the voltage difference with respect to the peak value of the current waveform, and the current waveform during normal operation of the microstructure. The capacity | capacitance change measuring apparatus of the micro structure of Claim 2 which is either the phase difference with respect to.   The capacitance change measurement of the microstructure according to any one of claims 1 to 3, wherein the voltage applying unit applies an alternating voltage whose level changes with time between the fixed part electrode and the movable part electrode. apparatus. A capacitance change measurement method for a microstructure including a fixed part electrode and a movable part electrode disposed opposite to the fixed part electrode and having a capacitance between the fixed part electrode,
Applying a voltage between the fixed part electrode and the movable part electrode;
Detecting a current flowing between the fixed part electrode and the movable part electrode when the voltage is applied;
And detecting a change in capacitance between the fixed part electrode and the movable part electrode based on the time change of the detected current.   Whether or not the measured microstructure operates normally based on whether or not the detected change in capacitance is within the measured value of the microstructure stored in advance during normal operation The method for measuring a change in capacitance of a microstructure according to claim 5, comprising a step of determining

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