JPH0798259A - Semiconductor sensor - Google Patents

Abstract

PURPOSE:To improve the durability of a sensor and to make it possible to change the characteristics arbitrarily by filling the space around a movable structure with a medium whose viscosity can be changed, and providing a viscosity control means. CONSTITUTION:When an inertial mass body 2 is displaced, the stress acting on a beam 4 is also changed. The resistance value of a piezoelectric resistor 6 is also changed. Thus, the stress acting on the beam 4 with the resistor 6 can be detected. In the internal space between an upper cover 8 and a lower cover 10, electric fluid 12, whose viscosity can be varied, is sealed. The sensor signal of the resistor 6 is inputted into an acceleration comparing circuit, wherein the signal is compared with the specified acceleration as a preset reference. When it is judged that the sensor signal exceeds the reference value, a voltage control circuit is actuated. The required voltage is applied to a control electrode 14. The viscosity of the fluid 12 is enhanced, and the control is performed so as to prevent the breakage of the mass body 2. Therefore, the rupture strength and the durability of the mass body 2 can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor sensor, and more particularly to a semiconductor sensor having a movable structure on a substrate.

[0002]

2. Description of the Related Art Conventionally, a semiconductor sensor in which a movable structure is formed on a semiconductor substrate has been used. In this type of semiconductor sensor, the beam that supports the movable structure is made of a very small thin film, so it is structurally easy to be destroyed by a displacement exceeding its strength or an external impact, and the device is There were problems with durability, reliability, yield deterioration during manufacturing, etc.

[0003]

In order to solve these problems, one having a structure (permanent magnet) for restricting the amount of displacement of the movable structure (see Japanese Patent Laid-Open No. 4-22833) and the movable structure. A proposal has been proposed in which the vibration displacement of the structure is attenuated by covering the periphery of the body with silicone oil (JP-A-2-32224). However, when the conventional devices described in these publications are applied to a sensor for measuring the displacement of a movable structure,
Displacement is regulated or attenuated, which significantly reduces the detection performance and detection range of the sensor, which is a practical problem. Therefore, the present invention has been made to solve the problems of the conventional technique, and an object thereof is to provide a semiconductor sensor having improved durability and capable of arbitrarily changing the characteristics.

[0004]

In order to achieve the above object, the present invention provides a semiconductor sensor in which a movable structure is disposed on a substrate, and a medium whose viscosity can be changed is filled around the movable structure and the medium of the medium is provided. It is characterized in that a viscosity control means for controlling so as to increase the viscosity is provided. In the present invention thus constituted, the durability is improved because the viscosity control means controls to increase the viscosity of the medium filled around the movable structure. Further, in the present invention, the medium is preferably an electromagnetic fluid, an electric fluid or liquid crystal. According to the present invention, the movable structure is a structure supported by a beam on a substrate. By arranging a plurality of control electrodes in parallel in the longitudinal direction of the beam and switching the energization to the plurality of control electrodes, The feature is that the substantial resonance frequency of the beam is changed. In the present invention configured as described above, by switching the energization to the plurality of control electrodes, the viscosity of the medium in the vicinity of the switched control electrodes is changed, thereby changing the substantial resonance frequency of the beam. To do. Thereby, the resonance frequency can be made variable.

Further, according to the present invention, it is preferable that the viscosity of the medium is increased by the viscosity control means when the displacement of the movable structure is a predetermined value or more. With this configuration, the viscosity of the medium is increased by the viscosity control means,
The displacement of the movable structure is prevented from exceeding a predetermined value. This makes it possible to prevent damage without impairing the sensor function. Further, in the present invention, it is preferable that the substrate is a silicon substrate, and the movable structure is integrally formed on the silicon substrate.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In this embodiment, the semiconductor sensor of the present invention is applied to an acceleration sensor. FIG. 1 is a sectional view showing an embodiment of the semiconductor sensor of the present invention. Figure 2
It is a block diagram for explaining operation of one example of a semiconductor sensor of the present invention. As shown in FIG. 1, reference numeral 1 is a silicon substrate, and an inertial mass body 2 is arranged on the silicon substrate 1 in a structure supported by a cantilever 4. The inertial mass 2 and the cantilever 4 are formed by anisotropic etching. The beam 4 is provided with a piezoresistor 6 where the stress is most concentrated. When the inertial mass body 2 is displaced, the stress acting on the beam 4 is also changed, so that the resistance value of the piezoresistor 6 is also changed. Thereby, the stress acting on the beam 4 by the piezoresistor 6 can be detected. An upper cover 8 and a lower cover 10 are arranged above and below the silicon substrate 1 so as to form a sealed space with the silicon substrate 1. The internal space formed by the upper cover 8 and the lower cover 10 is filled with an electric fluid 12, which is a variable viscosity fluid, so as to cover the inertial mass body 2. Here, the variable viscosity fluid is used as a general term for fluids whose viscosity can be changed by physical means.

Here, the electric fluid 12 means a fluid whose viscosity can be changed by applying an electric field, and specifically, a colloidal solution such as silica gel powder or starch corresponds to several kV / By applying an electric field of mm, the viscosity can be changed up to several hundred times. In addition to the electric fluid 12 described above, an isotropic inductive liquid or an anisotropic inductive liquid represented by magnetic fluid or liquid crystal can be used as the viscosity variable fluid. Here, the magnetic fluid is
A colloidal solution of magnetic particles means a fluid whose viscosity can be changed by an external magnetic field.
Further, a control electrode 14 for controlling the viscosity of the electric fluid 12 is provided on the inner surface side of the upper cover 8. The control electrode 14 has an acceleration comparison circuit 16 shown in FIG.
It is controlled by the voltage control circuit 18. The acceleration comparison circuit 16 stores a predetermined acceleration (upper limit value) serving as a reference thereof so as not to impair the performance of the sensor against an external impact. In addition, a high electric field is usually required to operate the electric fluid, but in this embodiment, since the device itself is minute, the electrode spacing for applying the electric field is on the order of several tens of μm, and therefore the applied voltage is high. Is low and convenient. Further, the encapsulation of the electric fluid 12 in such a minute space can be realized without any problem by adopting a process of encapsulating the fluid after vacuum deaeration, as in a liquid crystal cell manufacturing technique for a liquid crystal panel or the like.

Next, the operation of this embodiment will be described. As shown in FIG. 2, first, the sensor signal from the piezoresistor 6 is input to the acceleration comparison circuit 16. This acceleration comparison circuit 1
Reference numeral 6 compares the sensor signal with a predetermined acceleration (upper limit value) serving as a preset reference, and when it determines that the sensor signal exceeds the reference value, it activates the voltage control circuit 18 to set the required voltage. The electric fluid 1 is applied to the control electrode 14.
The viscosity of No. 2 is increased and the inertial mass 2 is controlled so as not to be damaged. On the other hand, when the acceleration comparison circuit 16 determines that the sensor signal does not exceed the preset predetermined reference acceleration, the sensor output is output as it is. When a magnetic fluid is used as the variable viscous fluid, a similar effect can be obtained by providing a magnetism generating means (coil or the like) instead of the control electrode 14 to control the current. As described above, in the present embodiment, the inertial mass body 2 is filled with the electric fluid 12 that is a variable viscosity fluid, and the inertial mass body 2 is applied to the electric fluid 12 by the control electrode 14.
The breaking strength and durability of the inertial mass body 2 can be improved by increasing the viscosity by applying an electric field that regulates the displacement. That is, when it is determined that the impact acting on the sensor exceeds a predetermined acceleration, which is the upper limit value, the electric field is instantaneously applied at a predetermined level to increase the viscosity of the electric fluid 12 to increase the viscosity of the inertial mass body 2. Displacement can be regulated and dampened to prevent breakage without impairing sensor performance.

Next, another embodiment of the present invention will be described with reference to FIGS. In this embodiment, the semiconductor sensor of the present invention is applied to control the detection characteristics of an acceleration sensor. FIG. 3 is a sectional view showing another embodiment of the semiconductor sensor of the present invention. FIG. 4 is a characteristic diagram showing a sensor output and a vibration frequency according to another embodiment of the present invention. Figure 5
FIG. 8 is a block diagram for explaining the operation of another embodiment of the semiconductor sensor of the present invention. This embodiment has the same basic structure as that shown in FIG. 1, but the control electrode provided on the upper cover 8 is different. That is, in this embodiment, a plurality (two in the embodiment shown in FIG. 3) of control electrodes 20 and 22 are arranged in parallel in the length direction of the beam at positions facing the portion of the beam 4 on the upper cover 8. It is provided. By applying an electric field between the control electrodes 20 and 22 and the beam 4, the viscosity can be locally changed. That is, in the acceleration sensor in which the inertial mass body 2 is supported by the beam 4 as in this embodiment, the resonance frequency is determined by the length of the beam,
The sensitivity of the sensor becomes maximum near this resonance frequency. Therefore, in the related art, as shown in FIG. 6, there is a device in which a plurality of elements having beams 30a, 30b, and 30c having different lengths are formed and a frequency analysis of vibration is performed. This conventional device has a problem in miniaturization and strict control of characteristics because a plurality of devices are formed. However, in this embodiment, the vibration frequency can be analyzed by electrically varying the resonance frequency of the sensor with one element unit.

The operation of this embodiment will be described below. In FIG. 4, A indicates a resonance frequency when the viscosity is not changed without applying an electric field between the control electrodes 20 and 22 and the beam 4, and B indicates a predetermined voltage applied between the control electrode 20 and the beam 4. Shows the resonance frequency of the case, C is the control electrode 22 and the beam 4
The resonance frequency is shown when a predetermined voltage is applied in between. First, when a predetermined voltage is applied between the control electrode 20 and the beam 4, the viscosity of the electric fluid 12 in the vicinity thereof increases and the displacement of the beam 4 is restricted at that portion. This is substantially the same as the length of the beam 4 is shortened, so that the resonance frequency can be shifted to the higher side, as shown by B in FIG. Similarly, when a predetermined voltage is applied between the control electrode 22 and the beam 4, the length of the beam 4 can be substantially further shortened, thereby changing the resonance frequency as shown by C in FIG. You can shift to a higher position. As described above, according to the present embodiment, the sensor characteristics can be easily changed by the electric means. Further, as shown in FIG. 5, in this embodiment, a plurality (n)
Control electrodes 24 are provided in parallel in the beam length direction, and a voltage switch control circuit 26 that switches the voltage applied to the plurality of control electrodes 24 at a fixed timing is provided. The sensor signal from the piezoresistor 6 is taken out and calculated by the calculation circuit 28,
The frequency frequency is analyzed and output. Therefore, the vibration frequency can be analyzed with a very simple structure.

[0011]

As described above, according to the semiconductor sensor of the present invention, the durability is improved and the characteristics can be arbitrarily changed.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor sensor of the present invention.

FIG. 2 is a block diagram for explaining the operation of one embodiment of the semiconductor sensor of the present invention.

FIG. 3 is a sectional view showing another embodiment of the semiconductor sensor of the present invention.

FIG. 4 is a block diagram for explaining the operation of another embodiment of the semiconductor sensor of the present invention.

FIG. 5 is a diagram showing sensor output and vibration frequency according to another embodiment of the semiconductor sensor of the present invention.

FIG. 6 is a partial plan view showing a beam portion of a conventional semiconductor sensor.

[Explanation of symbols]

 1 Silicon Substrate 2 Inertial Mass Body 4 Beam 6 Piezoresistive 8 Upper Cover 10 Lower Cover 12 Electric Fluid (Variable Viscosity Fluid) 14, 20, 22, 24 Control Electrode 16 Acceleration Comparison Circuit 18 Voltage Control Circuit 26 Voltage Control Switch Control Circuit 28 Arithmetic circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhiro Yoshimoto 3-1, Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Motor Corporation

Claims (5)

[Claims] 1. A semiconductor sensor having a movable structure arranged on a substrate, wherein a viscosity control means is provided around the movable structure to fill a medium whose viscosity can be changed and to increase the viscosity of the medium. Characteristic semiconductor sensor. 2. The semiconductor sensor according to claim 1, wherein the medium is an electromagnetic fluid, an electrofluid, or a liquid crystal. 3. The movable structure has a structure in which a substrate is supported by a beam, and a plurality of control electrodes are arranged in parallel in a longitudinal direction of the beam, and the energization of the plurality of control electrodes is switched. 2. The semiconductor sensor according to claim 1, wherein the substantial resonance frequency of the beam is changed by. 4. The semiconductor sensor according to claim 1, wherein the viscosity of the medium is increased by the viscosity control means when the displacement of the movable structure is a predetermined value or more. 5. The semiconductor sensor according to claim 1, wherein the substrate is a silicon substrate, and the movable structure is integrally formed on the silicon substrate.