JP2773460B2 - Semiconductor acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor,
In particular, it relates to a servo type semiconductor acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, a semiconductor acceleration sensor is mainly manufactured using a silicon substrate as a starting material. Due to the difference in acceleration detection principle, a piezo gauge is provided in silicon to read out the stress of a beam that deforms in proportion to the acceleration by using the change in its resistance value, and a movable type that displaces in proportion to the acceleration There are two types known in which an electrode is provided and a capacitor configured between the electrode and the electrode provided on the surface of the substrate reads the change in capacitance according to acceleration. The former is based on iTripleE Transactions on Electron Devices (IEEE)
TRANSACTIONS ON ELECTRON
DEVICES), VoL. ED-26, p. 191
1, 1979. The latter acceleration sensor using the change in capacitance has an advantage that it is easier to manufacture than the former sensor using piezoresistance. In other words, the former utilizes a change in capacitance of a capacitor made of a conductive material, while the former is manufactured through a high-precision impurity diffusion process such as ion implantation in order to manufacture an accurate piezo gauge. Therefore, a device that can be easily operated can be manufactured as long as the structure is made. An example of the structure is shown in FIG. This is disclosed in Japanese Unexamined Patent Publication No. Hei 1-2240865, and the transducer '89 (Transducer ') is disclosed.
89), sensors and actuators (S
sensors and Actuators), A21
-A23, 1990, P316-319. In this example, a silicon cantilever 55 similar to a piezo-type semiconductor acceleration sensor is used, and a structure in which the degree of freedom of movement of an acceleration detection system with respect to input acceleration is limited as much as possible. The input acceleration is applied to the weight portion serving as the movable electrode 51 and the upper and lower glass substrates 5.
The capacitance between the electrodes 52 and 53 provided on 4 is measured by a switched capacitor technique, and a control voltage by pulse width modulation (PWM) is applied to the electrodes 52 and 53 so that the deflection of the cantilever 55 becomes zero. I have. Since this control is an attractive force control using a force (attraction) of attracting positive and negative charges, two upper and lower electrodes are required. In previous servo type capacitance sensors, usually, a capacitance detection electrode and an electrode for controlling the movable electrode were separate, so a plurality of capacitor sets were provided, but in this example, the electrodes are shared by time division. Therefore, it has only two electrodes and has a simple structure. In this sensor, band 10
The one having about 0 Hz and the sensitivity of about 1 V / G is obtained.

[0003]

Conventionally, there is a sensor having a function of performing multi-axis acceleration detection using the piezoresistance effect. In general, a semiconductor is used as an element used for detecting acceleration and has non-linearity. For example, if the element has no nonlinearity, it is possible to detect only the acceleration along the x, y, and z axes by using a plurality of piezoresistive effect elements. However, the piezoresistive effect element has non-linearity, and since the non-linearity differs depending on the axis, even if the magnitude of the actually input acceleration is the same for each axis, the intensity changes. Then, there is a problem that the relative magnitude of the detected acceleration changes.

Further, since the conventional capacitive semiconductor acceleration sensor basically has only one pair of capacitors, it can measure acceleration of only one axis, and can measure acceleration of x, y, z axes by one sensor. Was impossible to measure.

Further, in a servo type semiconductor acceleration sensor having a feedback mechanism, if vibration other than an acceleration signal detectable by an electrode is input to the acceleration detection system, control becomes impossible. Only a sensor having a structure in which the resonance mode of the acceleration sensor that can be detected by a pair of capacitors placed in parallel with the weight is very large compared to other resonance modes that can be excited, ie, a cantilever structure sensor, can be put to practical use. There was a problem.

An object of the present invention is to provide a capacitive acceleration sensor capable of measuring accelerations on a plurality of axes.

It is another object of the present invention to enable a sensor having any structure, not limited to a cantilever, to perform servo feedback.

[0008]

A semiconductor acceleration sensor according to the present invention comprises a movable electrode provided on a support substrate and a movable electrode provided on the support substrate opposed to a position corresponding to an antinode of a resonance mode generated when the electrode resonates. A plurality of opposing electrodes provided on the substrate, a capacitor structure provided between the movable electrode and the support substrate, and means for performing a product-sum operation of voltages applied to the respective opposing electrodes and separating a vector component of acceleration. It is characterized by having.

Further, the semiconductor acceleration sensor of the present invention comprises a movable electrode provided on a support substrate and a plurality of electrodes provided on the support substrate facing positions corresponding to antinodes of resonance modes generated when the electrodes resonate. And a capacitor structure provided between a supporting substrate which is a movable electrode, means for separately detecting the capacitance between each counter electrode and the movable electrode, and each electrode according to a detection signal. Means for biasing

Further, in the present invention, there is provided a means for short-circuiting between the electrodes constituting the capacitor, and a third electrode is arranged with an insulator interposed between any one of the electrodes of the capacitor to form another capacitor. It is preferred to configure.

[0011]

In general, a vibration system has a small set of reference vibrations (vibration modes) that can describe any vibration generated in the vibration system. Under normal vibration, there is a clear difference in the amplitude of each reference vibration, and the vibration occurring in the vibration system is roughly described by using two or three of all sets of reference vibrations. It is possible to Therefore, by obtaining the small number of reference modes in advance using a known finite element method, arranging electrodes at positions of antinodes of each vibration mode, and forming a capacitor, all information of the vibration is obtained. It becomes possible. If this information is used as it is, a single sensor can detect acceleration in multiple axes, and by providing a circuit that applies a bias voltage to cancel each capacitance change and prevents deformation of the beam, all vibration modes can be detected. A servo-type semiconductor acceleration sensor that can operate stably with respect to the above can be manufactured. When actually performing multi-axis detection, a servo loop is constructed for each of the arranged electrodes, and control is performed so that the distance between the electrodes becomes a constant value. Then, a product-sum operation is performed on the voltages used for the control to detect acceleration along each axis. For example, when four capacitors are formed at four corners of a square, the voltages used to control the electrodes are V1, V2,
Assuming that V3 and V4 are set, an operation for obtaining the sum of the servo voltages V1, V2, V3 and V4 is performed to detect a state in which the vibrator for detecting acceleration vibrates perpendicularly to the sensor surface. When detecting the acceleration of the X-axis or the Y-axis, V1 + V2-V3-V4 or V1 + V3-
An operation is performed to obtain the voltage V2-V4. In addition, by storing the degree of shaft interference in a storage device in advance and using the data to correct the answer of the above calculation, more accurate acceleration measurement can be performed.

On the other hand, in the electrostatic type semiconductor acceleration sensor, a bias electrode is required above and below the movable electrode in order to apply a servo. However, when a voltage is applied to a capacitor formed by two electrodes, each of the bias electrodes is applied. This is because the electrode utilizes the generation of a force (attraction) in which the electrodes attract each other. However, there are two types of charge, plus and minus, and it should be possible to extract not only attractive force but also repulsive force. The former capacitor pulls each other because the two electrodes are biased positively and negatively, respectively, so that positive and negative surplus electric charges are formed on the surface of the material constituting each electrode, and the surplus electric charge forms an insulator. This is because they are going through each other. Therefore, another capacitor is formed between the two electrodes using the third electrode,
If a bias voltage can be applied between the two electrodes and the third electrode, the polarity is opposite to the third electrode, but a surface charge of the same polarity is generated on the two electrodes. And a repulsive force can be generated between the electrodes. This principle is exactly the same as the principle of electric detection.

[0013]

FIG. 1 is a plan view of a semiconductor acceleration sensor according to a first embodiment of the present invention. The movable electrode 9 includes the support 5
Are formed in the shape of a "field" supported by a beam 65 with the lower electrode 21a to 21d facing the four corners.

The structure of the semiconductor acceleration sensor will be described in more detail with reference to the manufacturing process diagram of FIG. 2 and referring to the manufacturing process.

First, as shown in FIG. 2A, a silicon substrate 1 serving as a substrate is prepared. Since this substrate simply functions as a support substrate, a substrate having a high resistance value or S
An OI wafer or an insulating substrate such as a glass substrate if the process permits. Here, a case where a silicon substrate is used will be described. Next, an oxide film 2 having a thickness of about 1 micron is deposited on the surface. Aluminum 3 serving as the lower electrode 21 is deposited thereon and patterned into an electrode shape. An oxide film 4 is deposited thinly to protect the movable electrode 9 from short-circuiting. Next, as shown in FIG. 2B, the oxide film 4 in a region 5 serving as a support portion of the movable electrode 9 is removed. Next, as shown in FIG. 2C, gold 7 serving as a sacrificial layer is deposited to a thickness of several thousand angstroms to several microns. Next, as shown in FIG. 2D, only the support portion 5 is etched to remove gold from the support portion. As shown in FIG. 2 (e), a conductive material (for example, Ti) 8 such as a metal to be a movable electrode 9 is deposited thereon from a thickness of several thousand angstroms to several microns to form a predetermined planar shape. I do. Finally, as shown in FIG. 2 (f), the gold 7 which is a sacrificial layer is removed by etching to form a space between the conductive material 8 and the oxide film 4 to obtain the movable electrode 9. FIG. 2F shows a cross section taken along line AA ′ of FIG.

FIG. 3 is a plan view with the movable electrode 9 removed, and the lower electrodes 21a to 21d are connected to an aluminum pad 23 for electrical exchange with the outside via a wiring 22. If the sensor is symmetric, the antinode positions of the resonance mode are also symmetric, so the lower electrodes 21a, 21b, 21c, 21d
Are similarly arranged symmetrically. Normally, considering the modes up to the third order, the first order is the vertical motion of the sensor weight, the second and third orders are the roll, so if at least four electrodes are provided as shown in FIGS. good. 24 is a contact electrode for supplying electricity to the movable electrode 9.

In order to perform a servo feedback operation with this sensor, first, the capacitance between the movable electrode 9 and each of the lower electrodes 21a to 21d is measured and compared with a reference value to perform error amplification. The amplified voltage is applied to each capacitor, and biasing is performed so that the capacitance becomes equal to the reference value. At this time, since the voltage applied to the capacitor is proportional to the acceleration signal input from outside, acceleration can be detected by extracting the voltage. Further, in order to perform multi-axis acceleration detection, it is necessary to perform a product-sum operation of voltages applied to the lower electrodes 21a to 21d. When actually performing multi-axis detection, a servo loop is constructed for each of the arranged electrodes, and control is performed so that the distance between the electrodes becomes a constant value. And
The sum of the voltages used for the control is calculated to detect the acceleration along each axis. For example, as in the present invention, 4
When two capacitors are formed, the lower electrode 21
The voltages used to control a to 21d are Va, V
Assuming b, Vc, and Vd, in order to detect a state in which the movable electrode vibrates in the vertical direction (z-axis) with respect to the substrate surface, an operation is performed to obtain the sum of the servo voltages Va, Vb, Vc, and Vd. When detecting acceleration in the X-axis or Y-axis direction, Va + Vb-Vc-Vd or Va + Vc-
An operation for calculating Vb-Vd is performed. In addition, the degree of shaft interference is stored in a storage device in advance, and the data is used to correct the answer of the above calculation, that is, by multiplying the correction value, more accurate acceleration measurement can be performed. .

In this embodiment, since the mass of the movable portion is very small as compared with the conventional sensor, a stable servo operation can be performed. In this embodiment, the four corners of the movable part are pressed, so that the movable part can be fixed stably.

FIG. 4 shows another embodiment. This embodiment is characterized in that it has a third electrode 35, and FIG.
Take the configuration shown in. The movable electrode 31 and the lower electrode 33 are electrically short-circuited, and have the same structure as the electric detection. Therefore, when actually used, a bias is used between these electrodes and the third electrode 35. Since static electricity has not only a repulsive force but also an attractive force, the movable electrode 31,
By freely controlling the voltage that can be applied to the lower electrode 33 and the third electrode 35, any force of the electrostatic force can be used. Servo feedback is performed as follows. When the movable electrode 31 moves in a direction approaching the third electrode 35 due to resonance due to the input acceleration, a repulsive force is applied between the two electrodes, and when the movable electrode 31 moves in a direction away from the third electrode 35, A bias is applied so that a suction force acts between the two electrodes so that there is no change in capacitance between the electrodes. The measurement of the interelectrode capacitance is performed by using a modulated bias voltage. In FIG. 4, 37
Is a silicon substrate, and 34 and 36 are oxide films.

Since the movable electrode of the sensor described above is made by lithography, it can be formed in various shapes such as not only a square but also a circle. However, symmetrical shapes such as circles and squares are easier to measure. When it is desired to increase the weight of the movable electrode in order to improve the sensitivity, a material having a high weight density may be deposited on the movable electrode.

As the sacrificial layer 7 shown in FIG. 2, a resist may be used instead of gold. However, when a resist is used, a substrate is heated to deposit a metal when a movable electrode is formed, or the deposited metal is deposited. Processing such as cleaning becomes difficult.

[0022]

According to the present invention, the servo type semiconductor acceleration sensor, which has been unstable in the past, can provide better stability and can simultaneously detect multi-axis acceleration. is there. In the conventional electrostatic servo acceleration sensor, it is necessary to dispose counter electrodes with the gap accurately set above and below the movable electrode, and it is necessary to use a complicated manufacturing process. 3
In the structure using the electrodes described above, since the electrodes need only be arranged on one side of the movable electrode, the manufacturing process becomes very easy. Further, a repulsion force that has not been used in a conventional semiconductor acceleration sensor can be used as the control force.
When the servo type is configured, the acceleration is measured by controlling the movable electrode so that it does not move even if acceleration is applied.
It goes without saying that it is possible to easily obtain an acceleration sensor having extremely good linearity without being affected by the non-linearity of the mechanical system. Therefore, there is an advantage that the problem of the non-linearity of the acceleration detection separation, which has been a problem in the conventional piezoresistance effect type multi-axis detection, is completely eliminated. Furthermore, in order to detect multi-axis by the conventional piezoresistive effect type, it was necessary to change the wiring of the piezoresistor, but in the present invention, since voltage signals are output from each electrode, simple signal processing is performed. Multi-axis acceleration can be detected simply by doing. In addition, a highly accurate electrostatic sensor can be obtained. In this specification, only the application to an acceleration sensor is described, but it goes without saying that the present invention can be applied to all devices controlled by electrostatic force.

[Brief description of the drawings]

FIG. 1 is a plan view showing a first embodiment of the present invention.

FIG. 2 is a view showing a manufacturing process of the first embodiment.

FIG. 3 is a plan view showing an electrode arrangement of the first embodiment.

FIG. 4 is a sectional view showing a second embodiment of the present invention.

FIG. 5 is a diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Oxide film 3 Aluminum 4 Oxide film 5 Support part 6 PAD area 7 Gold 8 Conductive material 9 Movable electrode 21 Lower electrode 22 Wiring 23 Aluminum pad 24 Contact electrode 31 Movable electrode 32 Oxide film 33 Lower electrode 34 Oxide film 35 Third electrode 36 Oxide film 37 Silicon substrate 51 Movable electrode 52 Upper electrode 53 Lower electrode 54 Glass substrate 55 Silicon cantilever

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01P 15/125 G01P 15/13 H01L 29/84

Claims (3)

(57) [Claims] 1. A movable electrode provided on a support substrate, a plurality of opposed electrodes provided on the support substrate facing a position corresponding to an antinode of a resonance mode generated when the electrode resonates, and a movable electrode A semiconductor acceleration sensor, comprising: a capacitor structure provided between a substrate and a support substrate; and means for performing a product-sum operation of voltages applied to respective counter electrodes and separating a vector component of acceleration. A movable electrode provided on the support substrate, a plurality of opposed electrodes provided on the support substrate facing positions corresponding to antinodes of a resonance mode generated when the electrode resonates, and a movable electrode. And a means for separately detecting the capacitance between each counter electrode and the movable electrode, and means for biasing each electrode according to a detection signal. A semiconductor acceleration sensor. 3. A capacitor having means for short-circuiting between electrodes constituting a capacitor, wherein an insulator is interposed between one of the electrodes of the capacitor and a third electrode is arranged to form another capacitor. The semiconductor acceleration sensor according to claim 1 or 2, wherein: