Patent Application
20110049653
1. Technical Field
The present invention relates to a micro-electromechanical systems (MEMS) sensor, a method of manufacturing an MEMS sensor, an electronic device, and so on.
2. Related Art
JP-A-7-301640 (FIGS. 1 and 20, hereinafter referred to as a related art document), for example, discloses a semiconductor acceleration sensor having a capacitance sensor and a detection circuit (a peripheral circuit) formed on a semiconductor substrate.
If the capacitance sensor and the detection circuit (the peripheral circuit) are formed on the semiconductor substrate, the chip size increases due to the detection circuit (the peripheral circuit). Further, the length of the wiring from the capacitance sensor to the detection circuit also increases. Since the detection signal output from the capacitance sensor is a minute electric current signal, if the signal is attenuated due to the impedance of the wiring, the detection accuracy of the detection circuit is degraded.
An advantage of some aspects of the invention is to reduce the occupied area of the MEMS sensor, for example, and prevent degradation of the detection sensitivity of the MEMS sensor, for example.
1. According to a first aspect of the invention, there is provided an MEMS sensor including a fixation frame section, a movable weight section coupled to the fixation frame section via an elastically deformable section and having a hollow section formed in a periphery, at least one fixed electrode section fixed to the fixation frame section and constituting one of electrodes of a capacitive element, at least one movable electrode section moving integrally with the movable weight section, disposed so as to be opposed to the fixed electrode section, and constituting the other of the electrodes of the capacitive element, and a detection circuit provided to the movable weight section and having an amplifier circuit adapted to amplify a signal from the capacitive element. Further, according to another aspect of the invention, there is provided an MEMS sensor including a fixation frame section, a movable weight section coupled to the fixation frame section via an elastically deformable section, a fixed electrode section extending from the fixation frame section toward the movable weight section, a movable electrode section extending from the movable weight section toward the fixation frame section, and disposed so as to be opposed to the fixed electrode section via a gap, a capacitance section composed mainly of the fixed electrode section and the movable electrode section, and an active element provided to the movable weight section.
In the aspect of the invention, the movable weight section is provided with the detection circuit. Since the detection circuit is provided, the mass of the movable weight section is increased accordingly, and therefore, the detection sensitivity of the physical quantity such as acceleration is improved.
Further, the movable electrode section is formed integrally with the movable weight section. Since the movable weight section is provided with the detection circuit, the length of the wiring connecting between the movable electrode section and an input node of the detection circuit becomes extremely small, and thus the attenuation of the current signal (the electrical charge signal) from the movable electrode section can be reduced. The detection circuit includes at least an amplifier circuit (which can include, for example, a first stage charge/voltage converter circuit and a voltage amplifier for amplifying a voltage signal), and is able to efficiently amplify the signal from the movable electrode section. The signal thus amplified is led to the fixation frame section via, for example, the wiring disposed along the elastically deformable section (the spring section). Since the voltage amplitude of the signal is large enough, the attenuation of the signal in this case due to the wiring impedance can substantially be neglected, for example.
2. According to a second aspect of the invention, in the MEMS sensor of the above aspect of the invention, the movable weight section includes a substrate provided with an impurity layer and a first laminate structure formed on the substrate, the first laminate structure includes a plurality of insulating layers stacked, and a first conductor layer as an electrode, and a second conductor layer as wiring, the impurity layer provided to the substrate and the first conductor layer provided to the first laminate structure constitute at least one active element as a constituent of the amplifier circuit adapted to receive a signal from the capacitive element, and an input node of the active element is connected to one of one and the other electrodes of the capacitive element via the second conductor layer. Further, according to another aspect of the invention, in the MEMS sensor of the above aspect of the invention, the movable weight section includes a substrate provided with an impurity layer and a first laminate structure disposed on the substrate, the first laminate structure includes an insulating layer and a first conductor layer, and the active element is mainly composed of the impurity layer and the first conductor layer. Further, the movable electrode section is formed using the first conductor layer, and the first conductor layer is connected to the movable electrode section and the active element using a second conductor layer.
In this aspect of the invention, the movable weight section includes, for example, the substrate provided with the impurity layer and the first laminate structure formed on the substrate. The first laminate structure can easily be formed using, for example, the semiconductor manufacturing technology (e.g., a multilayer wiring forming technology), and can include, for example, a plurality of insulating layers and the first conductor layer to form the electrodes of the elements (e.g., the element constituting the detection circuit), and the second conductor layer to form the wiring layer (e.g., the wiring layer for connecting the different elements to each other). The impurity layer provided to the substrate and the first conductor layer provided to the first laminate structure constitute a constituent of the amplifier circuit (e.g., the first stage amplifier circuit) included in the detection circuit, and the at least one active element (e.g., the MOS transistor in the input stage) for receiving the signal from the capacitive element. The input node (the gate in the case in which the active element is an MOS transistor) of the active element is electrically connected to the electrode of the capacitive element (either one of the two electrodes) via the second conductor layer as the wiring layer.
In the aspect of the invention, the substrate (e.g., a silicon substrate) can be used as a weight. Therefore, it is possible to effectively increase the mass of the movable weight section. Therefore, it is possible to improve the detection sensitivity of the physical quantity (e.g., acceleration). Further, the mass of the movable weight section can be adjusted by controlling the thickness of the substrate, and in this case, it becomes possible to make the structure design of the MEMS sensor easier. Further, the first laminate structure on the substrate itself (including the electrode layer and the wiring layer constituting the detection circuit) makes a contribution to increase in the mass of the movable weight section.
Further, the second conductor layer (which can be the wiring formed only of the conductor layer in the same layer level, or can be a multilayer wiring having conductor layers in the different layer levels connected to each other with contact plugs) as the wiring disposed in the first laminate structure constituting the movable weight section is used for connecting the output electrode of the capacitive element and the input node of the active element to each other. Since the wiring length of the wiring using the second conductor layer is allowed to be short, the wiring resistance is reduced, and the attenuation of the current signal (the electrical charge signal) from the capacitive element can be minimized. Therefore, degradation of the detection sensitivity due to the wiring impedance can be reduced.
3. According to a third aspect of the invention, in the MEMS sensor of the above aspect of the invention, the fixed electrode section is constituted by a second laminate structure, which can be formed using the same manufacturing method as that of the first laminate structure and is articulated to the fixation frame section, the second laminate structure is formed so as to project from the fixation frame section toward the hollow section, a conductor layer composed of a plurality of conductor layers provided to the second laminate structure coupled to each other to form a wall-like first conductor surface constitutes one of the electrodes of the capacitive element, the movable electrode section is constituted by a third laminate structure, which can be formed using the same manufacturing method as that of the first laminate structure and is articulated to the first laminate structure, the third laminate structure is formed so as to project from the first laminate structure toward the hollow section, and a conductor layer composed of a plurality of conductor layers provided to the third laminate structure coupled to each other to form a wall-like second conductor surface constitutes the other of the electrodes of the capacitive element.
In the aspect of the invention, an example of the structure of the fixed electrode section and the movable electrode section is described. The fixed electrode section is constituted by the second laminate structure, and the movable electrode section is constituted by the third laminate structure. The second laminate structure and the third laminate structure are manufactured using the same manufacturing method as that of the first laminate structure constituting the movable weight section. In one example, a laminate structure is formed on the substrate, and then the laminate structure is etched by selective anisotropic etching, thereby simultaneously forming the first laminate structure of the movable weight section, the second laminate structure projecting from the fixation frame section toward the hollow section, and the third laminate structure projecting from the first laminate structure toward the hollow section.
The second laminate structure is provided with the conductor layer having the first conductor surface. The conductor layer having the first conductor surface forms the fixed electrode (one of the electrodes of the capacitive element). The first conductor surface is, for example, a wall-like surface extending along the projection direction of the second laminate structure, and is an opposed surface (specifically, one of the opposed surfaces of the both electrodes disposed so as to face each other with a predetermined gap) of the capacitor. For example, in the case in which the laminated conductor layer (a conductor structural object having a predetermined width in the plan view) provided to the second laminate structure extends (is disposed) in the projection direction of the second laminate structure, it is possible to define the side surface section (i.e., the wall-like surface having a predetermined area) of the conductor structural object as the first conductor surface. The first conductor surface is covered by, for example, an insulating film (it should be noted that the first conductor surface can also be exposed).
In other words, as described above, the first conductor surface can be configured by, for example, coupling a plurality of conductor layers, and the conductor layer (which can be rephrased as a laminate conductor layer, a laminate conductor structure, or a conductor structural object (a conductor structure)) is composed of, for example, the conductor layers in the first through nth layers (n denotes a natural number equal to or larger than 2) and the contact plugs for connecting the respective conductor layers coupled integrally to each other, and the sidewall surface of the conductor layer (a laminate conductor layer, a laminate conductor structure, or a conductor structural object (a conductor structure)) thus integrally coupled to each other can be used as the first conductor surface.
Similarly, the conductor layer having a wall-like second conductor surface is provided to the third laminate structure, and the second conductor surface forms the movable electrode (the other of the electrodes of the capacitive element). The second conductor surface is, for example, a wall-like surface extending along the projection direction of the third laminate structure, and is an opposed surface (specifically, the other of the opposed surfaces of the both electrodes disposed so as to face each other with a predetermined gap) of the capacitor. For example, in the case in which the laminated conductor layer (a conductor structural object having a predetermined width in the plan view) provided to the third laminate structure extends (is disposed) in the projection direction of the third laminate structure, it is possible to define the side surface section (i.e., the wall-like surface having a predetermined area) of the conductor structural object as the second conductor surface. The second conductor surface is covered by, for example, an insulating film (it should be noted that the second conductor surface can also be exposed).
In other words, the second conductor surface can be configured by, for example, coupling a plurality of conductor layers, and the conductor layer is composed of, for example, the conductor layers in the first through nth layers (n denotes a natural number equal to or larger than 2) and the contact plugs for connecting the respective conductor layers coupled integrally to each other, and the sidewall surface of the conductor layer thus integrally coupled to each other can be used as the second conductor surface.
In the aspect of the invention, the conductor layers are stacked using the multilayer wiring technology, and then processed using photolithography to form the conductor surface (i.e., each of the electrodes of the capacitive element) having a wall-like side surface in a simultaneous parallel manner, which makes the manufacturing process easier.
4. According to a fourth aspect of the invention, in the MEMS sensor of the above aspect of the invention, the first laminate structure is provided with an isolated conductor layer isolated electrically, and functioning as a mass adjusting layer of the movable weight section. Further, according to another aspect of the invention, in the MEMS sensor of the above aspect of the invention, the first laminate structure is provided with a dummy wiring layer floating electrically.
In the aspect of the invention, the first laminate structure is provided with the isolated conductor layer (the dummy conductor layer as an adjustment layer of the mass) having no contribution to the signal transmission. The conductor material (typically metal) has a specific gravity larger than that of the insulating material. Therefore, according to the present aspect, the mass of the movable weight section can effectively be increased, thus the detection sensitivity of the physical quantity can be improved.
5. According to a fifth aspect of the invention, in the MEMS sensor of the above aspect of the invention, the first laminate structure is provided with an isolated conductor layer, which is composed of a plurality of conductor layers coupled to each other, which has a wall-like cross-sectional surface, which functions as the mass adjustment layer of the movable weight section and a electromagnetic shield member, and which is isolated electrically.
In this aspect of the invention, the first laminate structure is also provided with the isolated conductor layer having no contribution to the signal transmission. It should be noted that the isolated conductor layer is composed of a plurality of conductor layers coupled to each other, provided with a wall-like cross-sectional surface, and functions as the mass adjustment layer of the movable weight section and the electromagnetic shield member. The isolated conductor layer functions as the mass adjustment layer of the movable weight section, and at the same time functions as the electromagnetic shield layer. For example, the isolated conductor layer is disposed along the periphery of the movable weight section, and the detection circuit is disposed inside the area surrounded by the isolated conductor layer. Thus, an effect (an electromagnetic shield effect) of shielding the electromagnetic wave from the detection circuit or the electromagnetic wave to the detection circuit can be obtained.
6. According to a sixth aspect of the invention, there is provided a method of manufacturing an MEMS sensor including a fixation frame section, a movable weight section coupled to the fixation frame section via an elastically deformable section and having a hollow section formed in a periphery, at least one fixed electrode section fixed to the fixation frame section and constituting one of electrodes of a capacitive element, at least one movable electrode section moving integrally with the movable weight section, disposed so as to be opposed to the fixed electrode section, and constituting the other of the electrodes of the capacitive element, and a detection circuit provided to the movable weight section and having an amplifier circuit adapted to output a voltage signal varying in accordance with a capacitance variation of the capacitive element, the method including the steps of (p) forming a laminate structure on the substrate, the laminate structure having the detection circuit, the one and the other of the electrodes of the capacitive element, and wiring adapted to connect an input node of the amplifier circuit of the detection circuit to one of the one and the other of the electrodes of the capacitive element, (q) patterning the laminate structure formed on the substrate by anisotropic etching to form a first opening section forming an opening section adapted to expose a surface of the substrate, to sectionalize, by the first opening section, the fixation frame section, the elastically deformable section, the movable weight section coupled to the fixation frame section via the elastically deformable section, the movable electrode section projecting from the movable weight section toward the first opening section, and the fixed electrode section projecting from the fixation frame section toward the first opening section so as to be opposed to the movable electrode section, and (r) inserting an etchant via the first opening section to selectively perform anisotropic etching on the substrate to form a second opening section communicated with the first opening section and penetrating the substrate to form a hollow section composed of the first opening section and the second opening section to thereby separate the movable weight section and the movable electrode section from the fixation frame section. Further, according to another aspect of the invention, there is provided a method of manufacturing an MEMS sensor including the steps of (a) providing an impurity layer to a substrate, (b) forming a laminate structure including an insulating layer and a conductor layer on the substrate, (c) patterning the laminate structure using anisotropic etching to form a first opening section from an uppermost layer of the laminate structure to a surface of the substrate, and (d) injecting an etchant via the first opening section to selectively perform anisotropic etching on the substrate to thereby form a second opening section penetrating the substrate, thus forming a fixation frame section, a movable weight section coupled to the fixation frame section via an elastically deformable section, a fixed electrode section extending from the fixation frame section toward the movable weight section, a movable electrode section extending from the movable weight section toward the fixation frame section, and disposed so as to be opposed to the fixed electrode section via a gap, a capacitance section composed mainly of the fixed electrode section and the movable electrode section, and an active element provided to the movable weight section.
In the aspect of the invention, the laminate structure is formed on the substrate, and the laminate structure is patterned with the anisotropic etching to form the first opening section for exposing the surface of the substrate. Thus, the laminate structure is sectionalized into the fixation frame section, the elastically deformable section, the movable weight section, the movable electrode section, and the fixed electrode section. Subsequently, by the injection of the etchant through the first opening section, the anisotropic etching is selectively performed on the substrate to form the second opening section communicated with the first opening section and penetrating the substrate. Thus, the movable weight section and the movable electrode section are separated from the fixation frame section. Further, the hollow section is composed of the first opening section and the second opening section. Since the hollow section is formed around the movable weight section, it becomes possible for the movable weight section (and the movable electrode section) to be displaced in accordance with the deformation of the elastically deformable section (the spring section).
It should be noted that in the state in which the anisotropic etching is performed on the substrate to form the second opening section, the substrate also remains beneath the movable weight section, the movable electrode section, the fixed electrode section, and the elastically deformable section (the spring section). The substrate of the movable weight section has a contribution to the increase in the mass as described above. Further, the substrate in the movable electrode section and the fixed electrode section acts to prevent the deformation of the electrode sections such as warpage due to the difference in thermal expansion coefficient between the materials constituting the electrodes from occurring (thus, the area fluctuation of the capacitive element). The substrate in the movable weight section has a function as the adjustment layer of the damping factor (the factor representing the degree of the damping caused by the phenomenon that the vibration of the movable weight section is hindered due to the air resistance). Further, the substrate in the elastically deformable section has an effect of preventing unwanted displacement such as twist or swing caused when the elastically deformable section is deformed from occurring.
It should be noted that, for example, there is a case in which the substrate in the elastically deformable section can be eliminated, and in such a case, the substrate located under the elastically deformable section with a small wiring width can completely be removed by performing isotropic etching on the substrate for a predetermined period of time (although peripheral portion of the substrate in the movable weight section is removed by the isotropic etching, the substrate in the central portion of the movable weight section remains unremoved). The modification of the etching process such as addition thereof as described above can arbitrarily be performed. These modified examples are all included in the aspect of the invention.
7. According to a seventh aspect of the invention, there is provided an electronic device including either one of the MEMS sensors described above.
The MEMS sensor according to this aspect of the invention has advantages that it is compact in size because the detection circuit is integrated in the movable weight section, that it is highly sensitive since the capacitance variation of the capacitive element can be detected by the detection circuit disposed closely, that it is easily manufactured because the semiconductor manufacturing process can be applied, and that it is moderate in price. Therefore, the electronic device equipped with this MEMS sensor also enjoys substantially the same advantages.
The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.
Hereinafter, some preferred embodiments of the invention will be described in detail. It should be noted that the present embodiment explained below does not unreasonably limit the content of the invention as set forth in the appended claims, and all of the constituents set forth in the present embodiments are not necessarily essential as means for solving the problems of the invention.
Firstly, a configuration example of the MEMS sensor will be explained.
The capacitive acceleration sensor 100 includes a fixation frame section 110 (e.g., a silicon substrate), elastically deformable sections (spring sections) 130, a movable weight section 120 coupled to the fixation frame section 110 via the elastically deformable sections 130 with hollow sections 111, 113 formed in the periphery thereof, at least one fixed electrode section 150 fixed to the fixation frame section 110 and constituting one of electrodes of a capacitance section 145 (including a capacitive element C1 or a capacitive element C2), at least one movable electrode section 140 moving integrally with the movable weight section 120, and disposed so as to face the fixed electrode section 150, and constituting the other of the electrodes of the capacitance section 145 (the capacitive element C1 or the capacitive element C2), and a detection circuit 24 provided to the movable weight section 120. The detection circuit 24 has an amplifier circuit SA, to which signals (i.e., current signals (electrical charge signals) varying in accordance with the capacitance variation of the respective capacitive elements C1, C2)) from the capacitance sections 145 (the capacitive elements C1, C2) are input, and which amplifies the current signals (the electrical charge signals).
The movable electrode sections 140 are configured integrally with the movable weight section 120, and vibrates accordingly when the movable weight section 120 vibrates in response to the force caused by acceleration. In accordance thereto, the gaps (d) of the respective capacitance sections 145 (the capacitive elements C1, C2) are varied to vary the capacitance values of the respective capacitance sections (the capacitive elements C1, C2), and thus the migration of the charge is caused in accordance thereto. The value of the acceleration (a physical quantity) applied to the movable weight section 120 can be detected by amplifying the minute current caused by the migration of the charge by the amplifier circuit SA included in the detection circuit 24.
In the capacitive acceleration sensor 100 shown in
The detection circuit 24 includes at least the amplifier circuit SA. The amplifier circuit SA includes, for example, a first stage charge/voltage converter circuit and a voltage amplifier for amplifying a voltage signal, and is able to efficiently amplify the signal from the movable electrode sections 140. The signal thus amplified is led to the fixation frame section 110 via, for example, the signal wiring (not shown in
The amplifier circuit SA in the detection circuit 24 includes a charge (current)/voltage conversion amplifier (a Q/V conversion amplifier) 1 and an amplifier (a voltage amplifier) 2 of at least one stage for receiving the electrical signal (the voltage signal) output from the Q/V conversion amplifier 1.
The Q/V conversion amplifier 1 can be configured as, for example, a switched-capacitor amplifier having an operational amplifier and a switched capacitor combined with each other. The Q/V conversion amplifier 1 has a first stage active element (assumed here to be an MOS transistor M1 as an example) for receiving the detection signal input via the signal wiring L1. A MOS transistor M1 is (but not limited to) a differential pair transistor (one of the differential pair transistors) for constituting a differential pair of a differential amplifier circuit in the first stage of the operational amplifier (a differential amplifier).
The MOS transistor M1 has a source (S) and a drain (D) formed of, for example, an impurity layer (e.g., a diffusion layer) provided to the substrate, and a gate (G) made of, for example, polysilicon, silicide, or refractory metal disposed on a thin gate insulating film (not shown) formed on the substrate. Further, a source electrode E3 is connected to the source (S), a drain electrode E2 is connected to the drain (D), and a gate electrode E1 is connected (including the case in which the gate G itself functions as the gate electrode E1) to the gate G. The impurity layer and the electrodes constitute the MOS transistor M1.
Further, the signal wiring L1 electrically connects the other electrode CB of the capacitance section 145 (the variable capacitive element C1 or C2) and the gate (G) of the MOS transistor M1 to each other.
It should be noted that the detection circuit 24 can further include a signal processing circuit SPC disposed on the posterior stage of the amplifier circuit SA (but is not limited thereto, and the signal processing circuit SPC can also be provided to the fixation frame section 110). The signal processing circuit SPC can include, for example, a filter, an analog calibration circuit (e.g., a temperature compensation circuit) for compensating the temperature characteristic, an A/D converter circuit, a CPU, an interface circuit I/F.
As described above, the capacitive acceleration sensor 100 shown in
In other words, the movable weight section 120 includes, for example, the substrate provided with the impurity layer and the laminate structure formed on the substrate. Further, the first laminate structure constituting the movable weight section 120 can easily be formed using, for example, the semiconductor manufacturing technology (e.g., a multilayer wiring forming technology), and can include, for example, a plurality of insulating layers and the first conductor layer to form the electrodes (E1 through E3) of the elements (e.g., the element M1 constituting the detection circuit 24), and the second conductor layer to form the wiring layer (e.g., the wiring layer for connecting the different elements to each other, such as L1). The impurity layer provided to the substrate and the first conductor layer provided to the first laminate structure constitute the amplifier circuit (e.g., the first stage amplifier circuit) SA included in the detection circuit 24, and the at least one active element (e.g., the MOS transistor M1 in the input stage) for receiving the detection signals from the capacitance sections 145 (C1, C2).
The input node (the gate electrode E1 in the case in which the active element is the MOS transistor M1) of the active element is electrically connected to the electrode (either one of the two electrodes; the electrode CB in
It should be noted that although the case in which the first conductor layer included in the first laminate structure is used as the electrodes (E1 through E3) of the first stage MOS transistor M1 is explained above, this is nothing more than an example. The amplifier circuit SA is generally composed of a plurality of active elements (transistors) and a plurality of passive elements (e.g., resistors). It is deservingly possible to form the electrodes of each of these elements with the first conductor layer, and to constitute the wiring for electrically connecting these elements to each other with the second conductor layer. Further, each of the first conductor layer and the second conductor layer can be a conductor layer belonging to either one of the layers of the multilayer wiring structure, or can be a wiring structure having a multilayer structure composed of a plurality of conductor layers in different layers connected to each other with contact plugs.
According to the MEMS sensor (the capacitive acceleration sensor) 100 of the present embodiment, the substrate (e.g., a silicon substrate) can be used as the weight. Therefore, it is possible to effectively increase the mass of the movable weight section. Therefore, it is possible to improve the detection sensitivity of the physical quantity (e.g., acceleration). Further, the mass of the movable weight section can be adjusted by controlling the thickness of the substrate, and in this case, it becomes possible to make the structure design of the MEMS sensor easier.
Further, the first laminate structure on the substrate itself (including the electrode layer and the wiring layer constituting the detection circuit 24) makes a contribution to increase in the mass of the movable weight section 120. The mass of the movable weight section can be adjusted (further, the damping coefficient can also be possible at the same time) by controlling the thickness of the first laminate structure.
Further, the second conductor layer (which can be the wiring formed of the conductor layer of the same layer or the multilayer wiring composed of conductor layers in the different levels connected to each other with the contact plugs or the like as described above) as the wiring disposed in the first laminate structure constituting the movable weight section 120 can be used for connecting the output electrode CB of the capacitance sections 145 (the variable capacitive elements C1, C2) and the input node (E1) of the active element (MOS transistor M1) to each other. Since the detection circuit 24 can be disposed adjacent to the movable electrode sections 140, the length of the wiring L1 formed of the second conductor layer is allowed to be short. Therefore, it is possible to minimize the attenuation of the electrical charge signal (the current signal) from the capacitance sections 145 (C1, C2), and therefore, it becomes possible to prevent degradation of the detection sensitivity due to the wiring impedance.
When comparing
The detection circuit (an integrated circuit section) 24 is formed using, for example, a CMOS process. The detection circuit (the integrated circuit section) 24 can include the amplifier circuit SA, an analog calibration and A/D conversion circuit unit 26, a central processing unit (CPU) 28, and an interface (I/F) circuit 30. It should be noted that this configuration is nothing more than an example, and the invention is not limited to this configuration. For example, the CPU 28 can be replaced with a control logic circuit, and the A/D converter circuit can also be disposed in the output stage of the amplifier circuit SA. It should be noted that the A/D converter circuit and the CPU can also be disposed in another integrated circuit different from the detection circuit (the integrated circuit section) 24.
When the acceleration acts on the movable weight section 120 at rest, then the force due to the acceleration acts on the movable weight section 120, and the gaps of the respective pairs of movable and fixed electrodes are varied. If the movable weight section 120 migrates in the arrow direction shown in
The migration of the charge is caused in accordance with the variation of the capacitance values of the capacitors C1, C2. The amplifier circuit SA has a charge amplifier using, for example, a switched capacitor, and the charge amplifier converts a minute current signal caused by the migration of the charge into a voltage signal with a sampling action and an integral (amplifying) action. The voltage signal (i.e., a physical quantity signal detected by a physical quantity sensor) output from the amplifier circuit SA undergoes the calibration process (e.g., an adjustment of the phase and the signal amplitude, and possibly a low-pass filter process in addition thereto) by the analog calibration and A/D conversion circuit unit 26, and is then converted from the analog signal to the digital signal.
Here, an example of the configuration and the operation of the amplifier circuit SA will be explained with reference to
As shown in
As shown in
As shown in
It should be noted that the configuration example of the amplifier circuit SA described hereinabove is illustrative only, and the invention is not limited to this configuration. Further, although the two pairs of movable and fixed electrodes are only illustrated in
In the present embodiment, an example of a method of manufacturing a capacitive MEMS acceleration sensor will be explained. Hereinafter, an outline of the method of manufacturing the acceleration sensor module shown in
In the first process (process 1), the reverse surface of the semiconductor substrate (a silicon substrate) BS is selectively etched to adjust the thickness of the silicon substrate BS, and then the laminate structure including a plurality of conductor layers and a plurality of insulating layers is formed on the silicon substrate BS using a CVD method. Hereinafter, the process will specifically be explained step by step. In the following description, the structure of the CMOS transistor and the structure of the wiring provided to the laminate structure will be mentioned.
As shown in
It should be noted that the recess 102 provided to the reverse surface of the silicon substrate BS is not necessarily required. If the silicon substrate BS has an appropriate thickness from the beginning, the recess 102 is not required. However, it is preferable to appropriately control the thickness of the silicon substrate BS in accordance with the design value (the mass of the movable weight section) of the acceleration sensor, for example, and therefore, it is preferable to provide the recess 102. Further, if the recess 102 exists, a leg section with a step corresponding to the depth of the recess 102 can be formed. Therefore, it is preferable on the ground that the movable weight section 120 can be prevented from having contact with the installation surface.
Subsequently, the laminate structure 200 is formed on the silicon substrate BS using the semiconductor manufacturing technology. The laminate structure 200 includes a plurality of insulating layers INS0 through INS4 stacked in respective layers different from each other. In other words, the laminate structure 200 includes the insulating layer INS0 as a surface protective film, the interlayer insulating films INS1 through INS3, and the insulating layer INS4 as an ultimate protective film. Each of the insulating layers can be formed by depositing the material such as NSG, BPSG, SOG, or TEOS with a film thickness of 10,000 through 20,000 Å using the CVD process.
Further, in the laminate structure 200, the central portion corresponding to the movable weight section 120 corresponds to a first laminate structure YA, the portions corresponding to the fixed electrode sections 150 correspond to a second laminate structure YB, and the portions corresponding to the movable electrode sections 140 correspond to a third laminate structure YC. It should be noted that the laminate structure 200 is sectionalized or separated into the first laminate structure YA through the third laminate structure YC later by an etching process.
Further, the first laminate structure YA is provided with the first conductor layer to form the electrodes (including the contact plugs) of the active elements (e.g., transistors) and the passive elements (e.g., resistors) constituting the detection circuit 24, and the second conductor layer to form the wiring for electrically connecting different elements to each other using the multilayer wiring technology. The electrodes and the wiring can be formed by depositing a metal material (or silicide or polycide) such as Al, and then patterned by photolithography. Further, the contact plugs for connecting the electrode layers (or wiring layers) in different layers can be formed by, for example, plugging the through holes (embedded grooves) formed in the insulating layers with a conductive material such as W, TiW, or TiN using a sputtering or CVD process, and then removing the conductive material on the insulating layers using an etching-back process.
Further, in the example shown in
In
Further, as the conductor layer for constituting the multilayer wiring structure, there can be cited, for example, a contact plug MP1 embedded in the contact hole penetrating the insulating layers INS0 and INS1, second layer wiring layer ML2, a contact plug MP2 embedded in the contact hole (through hole) penetrating the insulating layer INS2, third layer wiring layer ML3, a contact plug MP3 embedded in the contact hole penetrating the insulating layer INS3, and fourth layer wiring layer ML4.
All of the gate electrodes E1a, Fib forming the gates G1, G2, the contact plug MP1, the second layer wiring layer ML2, the contact plug MP2, and the third layer wiring layer ML3 (parts thereof function as the source electrode E1 and the drain electrode E3 of the MOS transistor, respectively) can be called the first conductor layer for forming the electrodes of the MOS transistor.
Further, as shown in
Further, in
It should be noted that the dummy wiring layer DM (the isolated conductor layer) is composed of a part of the third layer wiring layer ML3, the contact plug MP3, and the fourth layer wiring layer ML4. As described above, the dummy wiring layer DM (the isolated conductor layer) has an advantage of increasing the mass of the movable weight section 120, and can function as a electro-magnetic shield member in some cases (this point will be described later).
In the second process (process 2), first opening sections 111a, 113a penetrating each of the insulating layers INS0 through INS4 constituting the laminate structure are formed. It should be noted that the first opening sections 111a are opening sections formed around the movable electrode sections 140 and the fixed electrode sections 150. The first opening sections 113a are opening sections formed around the sides not provided with the movable electrode sections 140 out of the four sides (in the case of the plan view) constituting the movable weight section 120. Although the first opening sections are separated into two opening sections 111a and 113a in accordance with the place where the opening sections are formed for the sake of convenience of explanation, these opening sections are formed at the same time, and it is also possible to recognize them as the same opening sections (either one of 111a and 113a).
The first opening sections 111a, 113a are formed by selectively patterning the insulating layers INS0 through INS4 using the anisotropic etching. The etching process is performed as, for example, the insulating film anisotropic etching in which the ratio (H/D) of the etching depth H (e.g., 4 through 6 μm) with respect to the opening diameter D (e.g., 1 μm) becomes a high aspect ratio. As an etchant of this anisotropic etching process, a mixed gas of, for example, CF4 and CHF3 can be used. According to this etching process, the laminate structure can be sectionalized into the fixation frame section 110, the movable weight section 120, and the elastically deformable sections 130. It should be noted that since the silicon substrate BS as a foundation is not processed, the sections are in the condition of being connected to the fixation frame section 110 with the silicon substrate BS.
In the third process (process 3), the etchant is injected via the first opening sections 111a, 113a provided to the laminate structure to perform the anisotropic etching selectively on the silicon substrate BS. By the anisotropic etching on the silicon substrate BS, the second opening sections 111b, 113b penetrating the silicon substrate BS are formed. The first opening sections 111a and the second opening sections 111b are communicated with each other to thereby form the hollow sections 111 around the movable weight section 120. Similarly, the first opening sections 113a and the second opening sections 113b are communicated with each other to thereby form the hollow sections 113 around the movable weight section 120.
As the anisotropic etching method for the silicon substrate BS, a method of performing etching while forming the sidewall protecting film, for example, can be used. As an example, the etching method using the inductively coupled plasma (ICP) disclosed in JP-T-2003-505869 can be adopted. In this method, a passivation step (sidewall protecting film formation) and the etching step are repeatedly executed to thereby form a protective film on the sidewall of the hole formed by etching, thus performing the anisotropic etching only in the depth direction while preventing the isotropic etching by the protective film. As etching conditions in the passivation step, it is preferable to use C4F8 or C3F6 as the etching gas under the process pressure of 5 through 20 par and the average input coupled plasma power of 300 through 1,000 W. As etching conditions in the etching step, it is preferable to use SF6 or ClF3 as the etching gas under the process pressure of 30 through 50 par and the average input coupled plasma power of 1,000 through 5,000 W. Besides the above, reactive ion etching (RIE) for performing the formation of the sidewall protecting film can also be used.
By forming the hollow sections 111, 113, the movable weight section 120 and the movable electrode sections 140 are separated from the fixation frame section 110. The movable weight section 120 is surrounded by the hollow sections (111 and 113), and is coupled to the fixation frame section at the four corners thereof with the elastically deformable sections 130. In other words, as a result, the movable weight section 120 is supported on the fly by the fixation frame section 110 via the elastically deformable sections 130 in a freely vibrating (fluctuating) state. Therefore, the movable weight section 120 (and the movable electrode sections 140) varies the position in accordance with the deformation of the elastically deformable sections 130, and is therefore able to vibrate along the direction of the acceleration applied thereto, for example.
In the hollow sections 111, the movable electrode sections 140 and the fixed electrode sections 150 are disposed so as to face each other. In other words, the movable electrode sections 140 are formed so as to project from the movable weight section 120 toward the hollow sections 111 in a plan view. Similarly, the fixed electrode sections 150 is formed so as to project from the fixation frame section 110 toward the hollow section 111.
In
In other words, the movable weight section 120 is composed of the substrate BS provided with the impurity layers (e.g., WE1, WE2, S1, D1, S2, and D2) and the first laminate structure. The first laminate structure includes, for example, a plurality of insulating layers (INS0 through INS4) formed in a stacked manner on the substrate BS, and also includes the first conductor layer (e.g., MP1, ML2, MP2, and ML3) as the electrodes (e.g., E1a, E2, and E3), and the second conductor layer (e.g., the third layer wiring layer ML3 drawn from the movable electrodes 140) as the wiring (e.g., the signal wiring L1 and other wiring). As a result, by the impurity layers (e.g., WE1, WE2, S1, D1, S2, and D2) provided to the substrate BS, the first conductor layer (e.g., MP1, ML2, MP2, and ML3), and so on, the amplifier circuit SA is composed, and at the same time, at least one active element (the MOS transistor, in this case) for receiving the detection signal from the capacitive element C1 (C2) is formed, and the input node (the gate G1) of the active element (the MOS transistor) is connected to one (CA, see
Further, as described above, the second laminate structures constituting the fixed electrode sections 150 are formed so as to project from the fixation frame section 110 toward the hollow sections 111, and are each provided with a conductor layer (a conductor structural object) having a wall-like first conductor surface. The wall-like first conductor surface AK1 (see the portion indicated by surrounding with the dotted line in the lower right part of
In other words, as described above, the first conductor surface AK1 can be formed by, for example, coupling a plurality of conductor layers, the conductor layer (the conductor structural object) is composed of, for example, the conductor layers (ML1 through ML4 in the example shown in
Further, the movable electrode sections 140 are formed using the same manufacturing method as that of the first laminate structure (and the second laminate structures for constituting the fixed electrode sections 150) for constituting the movable weight section 120 in a simultaneous parallel manner, and are constituted by the third laminate structures articulated (namely, formed so as to be integrally connected to each other) to the first laminate structure. The third laminate structures are formed so as to project from the first laminate structure constituting the movable weight section 120 toward the hollow sections 111.
The third laminate structures are each provided with a conductor layer (a conductor structural object) having a wall-like second conductor surface. The wall-like second conductor surface AK2 (see the portion indicated by surrounding with the dotted line in the lower left part of
The second conductor surface AK2 is, for example, a wall-like surface extending along the projection direction of corresponding one of the third laminate structures, and is an opposed surface (specifically, the other of the opposed surfaces of the both electrodes disposed so as to face each other with a predetermined gap GP, the movable electrode in this case) of the capacitor. For example, in the case in which the laminated conductor layer (a conductor structural object having a predetermined width W in the plan view) provided to each of the third laminate structures extends (is disposed) in the projection direction of the corresponding one of the third laminate structures, it is possible to define the side surface section (i.e., the wall-like surface having a predetermined area) of the conductor structural object as the second conductor surface. The surface of the second conductor surface AK2 is covered by, for example, a thin insulating layer (it should be noted that the invention is not limited thereto).
In other words, the second conductor surface AK2 can be formed by, for example, coupling a plurality of conductor layers, the conductor layer is composed of, for example, the conductor layers (ML1 through ML4 in the example shown in
The length (the electrode length) X1 of the opposed portion between the movable electrode sections 140 and the corresponding fixed electrode sections 150 is, for example, 150 μm, the electrode width W1 is, for example, 3 μm, the gap GP between the electrodes is, for example, 1.5 μm, the lateral width X2 of the movable weight 120 is, for example, 700 μm, and the length X3 of the side adjacent to both of the hollow sections 111, 113 is, for example, 1,000 μm. Further, the thickness h1 of the silicon substrate BS is, for example, 10 μm, and the height h2 of the laminate structure formed on the silicon substrate BS is, for example, 5 μm.
As described above, the movable weight section 120 is provided with the detection circuit 24 (including at least the amplifier circuit SA), and the signal output from the detection circuit is led to the circuit (not shown) provided to the fixation frame section 110 via the output wiring layer L2 disposed along the elastically deformable sections 130. In the upper right diagram in
In the capacitance MEMS sensor manufactured by the manufacturing method described above, the substrate BS remains in each of the movable weight section 120, the elastically deformable sections 130, the movable electrode sections 140 (and the fixed electrode sections 150). As described above, it is possible to form a part (e.g., an impurity layer) of the active element as a constituent of the detection circuit 24 by providing the silicon substrate BS to the movable weight section 120. It should be noted that the advantage provided by the substrate BS is not limited thereto. Specifically, since the substrate BS has a function as an adjustment layer for adjusting the characteristic of the MEMS sensor, the advantage that the manufacturing of a high-performance MEMS sensor becomes easier can be obtained in addition thereto. Hereinafter, advantages and so on of the substrate BS remaining in each of the sections will be considered in a comprehensive manner.
The MEMS acceleration sensor shown in
Further, the dummy wirings DM1 through MD4 extend in substantially parallel to the four sides, respectively, of the movable weight section 120 (having a quadrangle shape in the plan view), and are each formed of an isolated conductor layer having a wall-like surface (wall-like cross section) (the conductor layer having a multilayer wiring structure composed of a plurality of conductor layers at different layer levels coupled to each other by plugs). The dummy wirings DM1 through DM4 each have a contribution to efficiently increasing the mass of the movable weight section 120, and are further provided with an advantage as an electro-magnetic shield for shielding an electro-magnetic noise emitted from at least a part of the detection circuit 24 provided to the movable weight section 120 and at the same time shielding an electro-magnetic wave coming to the circuit from the outside, in addition thereto. Thus, there is obtained an advantage that the measure against the electro-magnetic noise in the detection circuit 24 (at least a part thereof) is improved, and the reliability of the circuit is enhanced.
In the lower part of
In the drawing, Z1 denotes a movable weight section region, Z2a denotes a movable capacitance electrode section region, Z2b denotes a fixed capacitance electrode section region, Z3 denotes an elastically deformable section region, and Z4 denotes a fixation frame section region.
In the movable weight section region Z1, beneath the laminate structure, there exists a member formed of a part of the silicon substrate BS with the same height (h20). In other words, as a result, the second movable weight section 120B (a mass adjustment section) is provided. As described above, the second movable weight section 120B formed of the silicon substrate BS as a foundation has a contribution to efficiently increasing the mass of the movable weight section 120 to thereby improve the sensitivity of the acceleration sensor.
Similarly, in the movable capacitance electrode section region Z2a, there is provided a second movable electrode section 140B (a damping factor adjustment section) formed of a part of the silicon substrate BS. By providing the second movable electrode section 140B (the damping factor adjustment section, with a height of h20), the overall height (h10+h20) of the movable electrode sections 140 can be adjusted, and thus, it becomes easy to adjust the damping factor D of the movable electrode sections 140 within an appropriate range. It should be noted that the significance of the damping factor D will be described later (see “Explanation of Parameters Related to Characteristics of MEMS Sensor”). Further, by providing the second movable electrode section 140B, warpage of the movable electrode due to the difference in thermal expansion coefficient between the materials of the laminate structure is suppressed. This is helpful for reducing the variation of the opposed area between a pair of capacitance electrodes. It should be noted that the fixed capacitance electrode section region Z2b is also provided with the second fixed electrode section 150B formed of a part of the silicon substrate BS.
Further, in the elastically deformable section region Z3, there are provided second elastically deformable sections (spring characteristic adjustment sections) 130B each formed of a part of the silicon substrate BS. In the elastically deformable sections (the spring sections) 130, unwanted motions such as twisting can be prevented by the second elastically deformable sections (the spring sections) 130B, and further, it is possible to set the mechanical spring constant to be sufficiently larger than the electrical spring constant (the spring constant caused by the electrostatic attractive force in the capacitance section) to thereby realize a desired linear spring characteristic.
Further, in the present embodiment, the laminate structure includes a plurality of conductor layers with different levels of layers, the insulating layers (INS0 through INS4) stacked one another, and the conductor layer as the dummy wiring (DM, DM1 through DM4). Thus, the laminate structure having a multilayer and dense structure including conductive materials and insulating materials is formed. Therefore, it is possible to effectively increase the mass (M) of the movable weight section 120. Further, as described above, it is also possible to assure the electrode sections of the capacitor having a predetermined opposed area in the laminate structure. Further, since the laminate structure can be formed using the manufacturing process (e.g., the CMOS process or the process of a bipolar/CMOS mixed IC) of a semiconductor device, it is easy to make the MEMS sensor and the detection circuit (the integrated circuit section) 24 coexist on the same substrate.
Further, as described above, it is possible to previously provide the recess 102 to the reverse surface of the substrate BS to thereby adjust the thickness of the substrate. In this case, by adjusting the depth of the recess, it is possible to previously adjust the thickness of the substrate portion. As described above, since the substrate is provided with a step by previously forming the recess 102, a space can be prepared under the movable weight section, and thus, the movable weight section can also be prevented from having contact with the installation surface.
Further, the damping factor D (i.e., the coefficient representing the significance of the action of the air resistance for suppressing the vibration of the movable weight section 120) can be set within an appropriate range due to the substrate BS (the second movable electrode section 140B) in the capacitance section 145. Further, since the adhesiveness between the substrate BS and the laminate structure is preferable, it is prevented that the warpage is caused by the difference in thermal expansion coefficient between the constituents of the laminate structure in response to the variation of the ambient temperature (the movable electrode with the warpage is illustrated by surrounding with the thick dotted line in the lower right diagram in
Further, as shown in the upper right diagram in
In the present embodiment, the MEMS sensor (here, the MEMS acceleration sensor) having a biaxial detection axis will be explained.
In the MEMS acceleration sensor 100 shown in
According to the several embodiments explained hereinabove, freedom of design is enhanced and the detection sensitivity of the physical quantity is also improved. Hereinafter, the parameters related to the characteristics of the MEMS sensor will specifically be explained. Denoting the overall capacitance of the electrode capacitor as C0, the spring constant of the elastically deformable section 130 as K, the inter-electrode gap as d0, the sensitivity S of the MEMS sensor is expressed as follows.
S=C0/d0·(M/K) [F/(m/sec2)]
In other words, the larger the mass of the movable weight section 120 is, the more the sensitivity is improved.
Further, the height of the movable electrode section and the fixed electrode section opposed to each other is denoted as h, the lateral length thereof is denoted as r, and the inter-electrode gap is denoted as d0. In this case, when the gap (the distance between the movable electrode section and the fixed electrode section) of the capacitor varies due to the movement of the movable electrode section, the gas between the electrodes moves up and down, and at that moment, damping (an action for stopping the vibration of the movable electrode section) is caused with respect to the movement of the movable electrode section due to the viscosity of the gas (the air). Denoting the number of pairs of electrodes as n, and the coefficient of viscosity of the gas as μ, the damping factor (D) representing the degree of the damping is expressed as follows.
D=n·μ·r(h/d0)3 [N·sec/m]
In other words, the damping factor D increases in proportion to the cube of the height (h) of the electrode section. Force is acted on the movable electrode section due to the Brownian movement of the gas, which causes the Brownian noise equivalent acceleration. The Brownian noise (BNEA) is expressed as follows, and the numerator of the expression is proportional to the square root of the damping factor (D) proportional to the cube of the height (h) of the movable electrode section.
BNEA=(√(4kBTD))/M [(m/sec2)/√Hz]
Further, since the capacitance MEMS sensor is a structure expressed by a motion equation (see e.g., the formula 1 below) of a free vibration with viscosity damping, it is necessary for the Q value and the resonance frequency (the characteristic frequency) of the structure to be designed to be preferable values. The resonance frequency (the characteristic frequency) ω of the structure performing a free vibration with viscosity damping is determined (see e.g., the formula 2 below) uniquely from the mass M of the movable weight section and the spring constant K of the springs (the elastically deformable sections) for supporting the movable weight section, and further, the Q value representing the sharpness of resonance can be determined (see e.g., the formula 3 below) from a calculating formula further involving the damping factor D. It should be noted that in the formula 3, ξ represents the critical damping coefficient.
As is obvious from the formula 3, if the mass M of the movable weight section is increased, the Q value increases, and if the damping factor D increases, the Q value decreases. If the height (i.e., the height of the movable electrode section) of the laminate structure is increased monotonically in order for increasing the mass M, the damping factor D increases in proportion to the cube of the height of the movable electrode section, and therefore, it becomes difficult to keep the Q value in the desired value. It should be noted that according to the embodiments of the invention described above, the modification of making the thickness of the substrate BS different between the movable weight section 120 and the movable electrode section 140, for example, is possible. Therefore, it is also possible to separate the mass M of the movable weight section and the damping factor D in the movable electrode section from each other to thereby independently control the mass M and the damping factor D. Therefore, it is possible to easily perform setting of the damping factor D of the movable electrode section to an appropriate value while keeping the Q value in an appropriate value.
Further, by forming the second elastically deformable section made of the substrate material, the movement of the first elastically deformable section constituted by the laminate structure in the unwanted direction (e.g., a vertical direction) is prevented, and thus the possibility of causing the unwanted movement such as twisting can be reduced. By preventing the unwanted deformation in the elastically deformable sections (the spring sections), the detection sensitivity of the MEMS sensor can further be improved.
Further, it is necessary to make the value of the spring constant in the elastically deformable sections (the spring sections) fall within an appropriate range in order for assuring the desirable resonance characteristic in the vibration section. The effective spring constant is not determined only by the mechanical spring constant of the elastically deformable sections (the spring sections), but is determined comprehensively also taking the electrical spring constant caused by the electrostatic force (the coulomb force) acting between the fixed electrode and the movable electrode in the capacitance electrode section into consideration. Specifically, the effective spring constant is determined by “(mechanical spring constant)−(electrical spring constant).” Therefore, unless the design is made so that the electrical spring constant becomes sufficiently smaller than the mechanical spring constant, it becomes that the formula of the linear spring characteristic expressed as follows is not satisfied, and this point causes constraint on the design.
F=kX (F denotes the force, k denotes the spring constant, and X denotes the displacement)
In contrast, if the structure (the structure in which the silicon substrate material is actively used to thereby optimize the characteristics of the constituents) of the invention is adopted, the value of the lateral width (the length in the lateral direction) of the electrode section can be suppressed to, for example, about 130 μm, which can be fit into the feasible length (within an appropriate range which can be used in the typical design). Further, at the same time, the relationship of (electrical spring constant)<<(mechanical spring constant) can be satisfied due to the rigidity of the second elastically deformable section 130B (see
Although the present embodiment is hereinabove explained in detail, it should easily be understood by those skilled in the art that various modifications not substantially departing from the novel matters and the effects of the invention are possible. Therefore, such modified examples should be included in the scope of the invention. For example, a term described at least once with a different term with a broader sense or the same meaning in the specification or the accompanying drawings can be replaced with the different term in any part of the specification or the accompanying drawings.
For example, the MEMS sensor according to the invention is not necessarily limited to those applied to capacitance acceleration sensors, but can also be applied to piezoresistive acceleration sensors. Further, the MEMS sensor according to the invention can also be applied to physical sensors for detecting the variation of the capacitance caused by the movement of the movable weight section. The MEMS sensor according to the invention can be applied to, for example, gyro sensors, or silicon diaphragm type pressure sensors. For example, in the pressure sensor for deforming the silicon diaphragm by the air pressure in the cavity (a hollow chamber), and detecting the variation (or the variation of the resistance of the piezoresistance) of the capacitance due to the deformation, if at least a part of the detection circuit is provided to the silicon diaphragm, the detection sensitivity can be improved.
Further, in the MEMS sensor according to an aspect of the invention, at least the level of the physical quantity can be detected by adopting the opposed electrodes distance of which is variable. It should be noted that the direction in which the physical quantity acts is not detectable with one capacitance. Therefore, it is preferable to provide at least one fixed electrode section, and a plurality of movable electrode sections formed integrally with the movable weight section and moving in at least one axial direction to increase and decrease the distance from the at least one fixed electrode section. This is because, when the plurality of movable electrode sections moves with the movable weight section with respect to the at least one fixed electrode section, one of the two inter-electrode distances increases while the other thereof decreases, thereby the level and the direction of the physical quantity can be detected from the level and the relationship between increase and decrease of the capacitances depending on the inter-electrode distances. Further, the detection axis of the physical quantity is not limited to the uniaxial detection axis or the biaxial detection axis described above, but can be a multiaxial detection axis with three or more axes can also be adopted. Further, it is also possible to adopt a method of detecting the physical quantity using the variation of the opposed area between the electrodes of the capacitor.
The entire disclosure of Japanese Patent Application No. 2009-195121, filed Aug. 26, 2009 is expressly incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-195121 | Aug 2009 | JP | national |
