JP2010214588A - Mems device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microelectromechanical system (MEMS) device for reducing parasitic capacity between a MEMS structure and a semiconductor substrate. <P>SOLUTION: The MEMS device 1 has the MEMS structure 30 having a fixed electrode 20 and a movable electrode 26 formed on the semiconductor substrate 10 via an insulating layer. A well 13 is formed on the semiconductor substrate 10 under the fixed electrode 20, and the well 13 of impressing positive voltage on the fixed electrode 20 is a p type well. The voltage is impressed on the well 13 so that the well 13 becomes a depleted state. With this voltage, the depleted state is maintained. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a MEMS device having a MEMS structure on a semiconductor substrate.

  In recent years, attention has been paid to MEMS devices manufactured using MEMS (Micro Electro Mechanical System) technology. A MEMS device is used for applications such as sensors and vibrators by manufacturing a minute MEMS structure on a semiconductor substrate. The MEMS structure is provided with a fixed electrode and a movable electrode, and a characteristic as a MEMS device is obtained by detecting capacitance generated in the fixed electrode by utilizing the bending of the movable electrode.

In general, there are cases where a circuit capacitor such as an IC includes a parasitic capacitance, which is known to adversely affect the electrical characteristics of the IC. This parasitic capacitance is also generated in the MEMS device, and the influence on the electrical characteristics due to the parasitic capacitance becomes conspicuous with the narrowing of the electrodes between the MEMS structures and the increase of the applied frequency.
A MEMS structure manufactured by a surface MEMS method in which an extremely thin oxide film or nitride film is formed on a semiconductor substrate and a MEMS structure is directly formed on the oxide film is formed on a semiconductor substrate even if the area occupied by the structure is small. Parasitic capacitance is easily formed between the substrate and the substrate.
In particular, in the case of an electrostatic MEMS device that detects capacitance displacement caused by mechanical displacement of the movable electrode, the output signal is very weak, and the absolute value of the capacitance displacement is not sufficiently large with respect to the parasitic capacitance. Therefore, it is susceptible to parasitic capacitance.
In addition, when the parasitic capacitance is large and the resistance of the substrate surface is low, or when the opposing capacitance between the substrate and the electrode is large, the signal leaks from other than the original path through carriers excited on the substrate surface. Cheap.

For example, as shown in FIG. 16, a MEMS device in which an oxide film 111 and a nitride film 112 are formed on a semiconductor substrate 110 and a MEMS structure is formed thereon is known. This MEMS device includes a fixed electrode and a movable electrode, and is provided with an input side electrode 113, an output side electrode 114, a drive electrode 115 as fixed electrodes, and a movable portion 116 connected to the input side electrode 113 as a movable electrode.
In the MEMS device having such a structure, a high frequency signal may leak from the input side electrode 113 to the output side electrode 114 through the surface of the semiconductor substrate 110.
In order to solve this problem, Patent Document 1 discloses that the lower electrodes of the transducer elements (MEMS structure) are collectively connected together to reduce the area on the substrate occupied by the high-frequency signal wiring. The content of reducing the amount of leakage to the substrate is disclosed.

JP 2006-174174 A (5 pages, lines 7 to 11)

However, reducing the occupied area of the MEMS structure as described above is an effective method for reducing the parasitic capacitance, but it may be difficult to reduce the occupied area due to design and manufacturing restrictions. For this reason, when the occupation area of the MEMS structure cannot be reduced, there is an adverse effect on the characteristics of the MEMS device due to the parasitic capacitance.
The present invention has been made to solve the above-described problems, and an object thereof is to provide a MEMS device that reduces the parasitic capacitance between the MEMS structure and the semiconductor substrate.

  In order to solve the above-described problems, a MEMS device according to the present invention is a MEMS device including a MEMS structure having a fixed electrode and a movable electrode formed on a semiconductor substrate via an insulating layer, When a well is formed in the semiconductor substrate below the electrode, and a positive voltage is applied to the fixed electrode, the well is a p-type well, and a negative voltage is applied to the fixed electrode The well is an n-type well.

According to this configuration, the well is formed in the semiconductor substrate below the fixed electrode in the MEMS structure, and when a positive voltage is applied to the fixed electrode of the MEMS structure, the well is a p-type well, and the MEMS structure When a negative voltage is applied to the fixed electrode, the well is an n-type well.
Thus, by forming the well, the surface of the semiconductor substrate on which the well is formed is depleted, and the apparent distance between the counter electrodes is increased by the depletion layer, so that the parasitic capacitance of this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high frequency signal does not leak through the surface of the semiconductor substrate, and the characteristics of the MEMS device can be stabilized.

  In the MEMS device of the present invention, it is desirable that a voltage is applied to the well so that the well is depleted.

According to this configuration, a voltage is applied to the well so that the well formed in the semiconductor substrate below the fixed electrode is depleted.
When a voltage having a large absolute value is applied to the fixed electrode, an inversion layer is generated on the surface of the semiconductor substrate in the well and electrons are excited. In this state, signal leakage on the surface of the semiconductor substrate tends to occur regardless of the depletion capacity. Therefore, if a voltage having a value obtained by subtracting a voltage at which the well is depleted from the voltage applied to the fixed electrode is applied to the well, the well can maintain the depletion state, and the inversion layer is formed on the surface of the semiconductor substrate of the well It is possible to prevent the electrons from being excited and excited.
As described above, since the well can maintain a depletion state, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high-frequency signal does not leak through the surface of the semiconductor substrate. The characteristics of the MEMS device can be stabilized.

  In the MEMS device of the present invention, the semiconductor substrate is a p-type substrate and the well is an n-type well, and the bias voltage of the MEMS structure is Vp, and the voltage applied to the well below the MEMS structure Is Vwell, and the threshold voltage at which the inversion layer is generated in the well is Vth, it is desirable that Vp <0, Vwell ≧ 0, and 0 <| Vp−Vwell | <| Vth |.

  By satisfying the above conditions as described above, when the semiconductor substrate is a p-type substrate and the well is an n-type well, the well formed in the semiconductor substrate below the fixed electrode is depleted. Further, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high frequency signal does not leak through the surface of the semiconductor substrate, and the characteristics of the MEMS device can be stabilized.

  In the MEMS device of the present invention, the semiconductor substrate is an n-type substrate and the well is a p-type well, the bias voltage of the MEMS structure is Vp, and the voltage applied to the well below the MEMS structure Is Vwell, and the threshold voltage at which the inversion layer is generated in the well is Vth, it is desirable that Vp> 0, Vwell ≦ 0, and 0 <| Vp−Vwell | <| Vth |.

  By satisfying the above conditions as described above, when the semiconductor substrate is an n-type substrate and the well is a p-type well, the well formed in the semiconductor substrate below the fixed electrode is depleted. Further, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high frequency signal does not leak through the surface of the semiconductor substrate, and the characteristics of the MEMS device can be stabilized.

  In the MEMS device of the present invention, the MEMS device includes a MEMS structure having a fixed electrode and a movable electrode formed on a semiconductor substrate via an insulating layer, the MEMS device being provided below the fixed electrode. A well having the same polarity as that of the semiconductor substrate is formed in the semiconductor substrate, and a separation well is formed that surrounds the well in the semiconductor substrate and has a polarity opposite to that of the well. Or between the separation well and the semiconductor substrate so as to have a reverse bias.

  According to this configuration, the potential of the semiconductor substrate and the well can be separated, the MEMS structure can be operated at a high voltage in absolute value, and the parasitic capacitance between the MEMS structure and the semiconductor substrate is reduced. be able to. Further, if such a configuration is adopted, the potential of the well does not affect the potential of the semiconductor substrate, so that the MEMS structure and a circuit such as an IC can be used in an integrated manner.

  In the MEMS device of the present invention, the semiconductor substrate is a p-type substrate, the well is a p-type well, and the separation well is an n-type well, and the bias voltage of the MEMS structure is Vp, and the MEMS structure It is preferable that Vp> 0 and 0 <Vp−Vwell <Vth are satisfied, where Vwell is a voltage applied to the well below V and Vth is a threshold voltage at which an inversion layer is generated in the well. .

  By satisfying the above conditions as described above, when the semiconductor substrate is a p-type substrate, the well is a p-type well, and the separation well is an n-type well, the well formed in the semiconductor substrate below the fixed electrode is depleted. It becomes a state. Further, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high frequency signal does not leak through the surface of the semiconductor substrate, and the characteristics of the MEMS device can be stabilized.

  In the MEMS device of the present invention, the semiconductor substrate is an n-type substrate, the well is an n-type well, and the separation well is a p-type well, and the bias voltage of the MEMS structure is Vp, and the MEMS structure It is preferable that Vp <0 and 0 <Vp−Vwell <Vth are satisfied, where Vwell is a voltage applied to the well below and Vth is a threshold voltage at which an inversion layer is generated in the well. .

  By satisfying the above conditions as described above, when the semiconductor substrate is an n-type substrate, the well is an n-type well, and the separation well is a p-type well, the well formed in the semiconductor substrate below the fixed electrode is depleted. It becomes a state. Further, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and a high frequency signal does not leak through the surface of the semiconductor substrate, and the characteristics of the MEMS device can be stabilized.

The structure of the MEMS device in 1st Embodiment is shown, (a) is a partial schematic plan view of a MEMS device, (b) is a partial schematic cross section along the AA disconnection of (a). The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 1st Embodiment. The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 1st Embodiment. The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 1st Embodiment. FIG. 10 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 1. The graph which shows the relationship between the difference (Vp-Vwell) of Vp and Vwell in the modification 1, and the capacity | capacitance C between a MEMS structure and a well. FIG. 10 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 2. The graph which shows the relationship between the difference (Vp-Vwell) of Vp and Vwell in the modification 2, and the capacity | capacitance C between a MEMS structure and a well. The structure of the MEMS device in 2nd Embodiment is shown, (a) is a partial schematic plan view of a MEMS device, (b) is a partial schematic cross section along the BB disconnection of (a). The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 2nd Embodiment. The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 2nd Embodiment. The typical fragmentary sectional view which shows the manufacturing process of the MEMS device in 2nd Embodiment. The structure of the MEMS device in 3rd Embodiment is shown, (a) is a partial schematic plan view of a MEMS device, (b) is a partial schematic cross section along CC disconnection of (a). FIG. 10 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 3. FIG. 12 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 4. Explanatory drawing explaining the state of the signal leakage in the conventional MEMS device.

Prior to the description of the embodiments of the present invention, for the understanding of the present invention, the principle that a parasitic capacitance occurs in a semiconductor substrate and a signal leaks from other than the original path will be described.
First, the above phenomenon can be explained using a capacitor in which a metal is formed on a semiconductor via an insulator as a model. A MOS capacitor using a p-type semiconductor will be described as an example.
In the capacitance-voltage characteristics of a MOS capacitor using a p-type semiconductor, an accumulation state is applied when the gate voltage is negative, a depletion state is applied when a positive voltage is applied to the gate voltage, and a large positive voltage is applied to the gate. In some cases, it is known to be in an inverted state.
In the accumulation state, carriers (holes) are generated on the substrate surface, the conductor resistance near the substrate surface is lowered, and signal leakage in the lateral direction is likely to occur.
Further, in the depletion state, the apparent distance between the counter electrodes is increased, so that the parasitic capacitance in this portion is reduced, carriers are not generated in the vicinity of the substrate surface, and signal leakage in the lateral direction is less likely to occur.
Further, in the inversion state, an inversion layer is formed on the substrate surface, and carriers having opposite signs are excited here, and signal leakage in the lateral direction is likely to occur on the substrate surface.

Thus, in the depletion state, signal leakage in the lateral direction hardly occurs on the substrate surface. Since the MEMS device generally operates at a high voltage, the higher the voltage (threshold voltage) value generated by the inversion layer is, the less likely signal leakage occurs on the substrate surface.
In addition, when a well is formed in a semiconductor substrate, an inversion layer is less likely to be generated up to a higher applied voltage when a voltage is applied to the substrate surface.
The voltage generated by the inversion layer in the MOS capacitor can be expressed by a threshold voltage derivation formula of the MOS transistor. The threshold voltage Vt when a p-type well is used is shown in equation (1).

ここで、 ｋ：ボルツマン定数
Ｔ：温度
ｑ：電荷の絶対値
Ｎ_A：アクセプタ濃度
ｎ_i：真性キャリア濃度
Ｃ_i：絶縁膜の単位面積あたりの容量
ε₀：真空中の誘電率
ε_S：絶縁膜の比誘電率
この式によれば、反転が始まるしきい値電圧は半導体基板部分のアクセプタ濃度に依存することがわかる。アクセプタ濃度はウェルのキャリア濃度でほぼ近似できることから、キャリア濃度が大きいほど、高い電圧までＭＯＳキャパシタが空乏状態を維持することが可能であるのがわかる。
またウェルを形成せずにｐ型シリコン基板をそのまま使用した場合について考えると、基板のキャリア濃度がウェル形成時よりも小さくなるために、式（１）によれば反転層が生ずる電圧が低くなり、空乏状態で使用できる電圧範囲が狭くなることが理解できる。
この様に、ウェルを形成することで、より広い電圧範囲でＭＥＭＳデバイスへの寄生容量の削減が可能となる。
さらに、ウェルを形成する場合は用いる基板種類（ｐ型基板若しくはｎ型基板）によらず最適な基板構造をＭＥＭＳ構造体の固定電極下方に設けることが可能であり、用いる基板種類によらず寄生容量の抑圧が可能となる。

Here, k: Boltzmann constant T: Temperature q: Absolute value of charge N _A : Acceptor concentration n _i : Intrinsic carrier concentration C _i : Capacity per unit area of insulating film ε ₀ : Dielectric constant in vacuum ε _S : Insulation According to this equation, it can be seen that the threshold voltage at which inversion begins depends on the acceptor concentration of the semiconductor substrate portion. Since the acceptor concentration can be approximated by the carrier concentration of the well, it can be seen that the higher the carrier concentration, the more the MOS capacitor can be kept in a depletion state.
Considering the case where a p-type silicon substrate is used as it is without forming a well, the carrier concentration of the substrate is smaller than that at the time of forming the well, so that the voltage generated by the inversion layer is reduced according to equation (1). It can be understood that the voltage range that can be used in the depletion state becomes narrow.
In this way, by forming the well, it is possible to reduce the parasitic capacitance to the MEMS device in a wider voltage range.
Further, when forming a well, an optimum substrate structure can be provided below the fixed electrode of the MEMS structure regardless of the substrate type (p-type substrate or n-type substrate) to be used. Capacity suppression is possible.

As described above, by forming a well in the semiconductor substrate, the voltage generated in the inversion layer can be increased and signal leakage on the substrate surface can be suppressed.
In addition, it is known that an n-type semiconductor substrate causes an accumulation state, a depletion state, and an inversion state by a gate voltage. As in the above, parasitic capacitance is reduced by using the depletion state, and the vicinity of the substrate surface No carrier is generated, and signal leakage in the lateral direction is less likely to occur.

Next, specific device characteristics when the MEMS structure is operated in a depleted state below the fixed electrode will be described. Here, the effect when applied to a MEMS vibrator will be described as an example.
When the MEMS vibrator is operated with the semiconductor substrate being depleted as described above, the parasitic capacitance value formed decreases, and therefore, the amount of signals passing through these parasitic capacitances decreases, so the resonance peak is steep. It becomes.
Further, when the oscillation circuit is configured by connecting to the active circuit, the parasitic capacitance included in the MEMS vibrator is equivalently regarded as the parasitic capacitance included in the transistor, and thus the negative resistance that can be generated by the transistor is reduced. It is known. Therefore, if the parasitic capacitance of the MEMS vibrator is reduced, the negative resistance value that can be generated with respect to the capability of the transistor is increased, so that the power consumption of the circuit can be reduced.
On the other hand, when the well is not configured, the bias voltage that can be applied to the MEMS vibrator decreases. When a bias voltage higher than a threshold value is applied to the MEMS vibrator, the substrate under the fixed electrode of the MEMS structure is in an inverted state, so that electrons that are minority carriers are excited on the substrate surface, and a signal flows in the lateral direction. It becomes easy. In addition, since the parasitic capacitance between the fixed electrode and the substrate also increases, the parasitic capacitance of the MEMS vibrator increases equivalently. As a result, problems such as the resonance peak of the vibrator becoming dull (Q value deterioration) occur.
As described above, it has been described that the electrical characteristics of the MEMS structure can be improved by using the substrate below the fixed electrode of the MEMS structure in a depleted state.
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described with reference to the drawings.
(First embodiment)

  FIG. 1 shows the configuration of the MEMS device of the present embodiment, FIG. 1 (a) is a partial schematic plan view of the MEMS device, and FIG. 1 (b) is a partial schematic sectional view taken along the line AA in FIG. 1 (a). It is.

The MEMS device 1 includes a MEMS substrate 30 formed on a semiconductor substrate 10, a wiring layer 27 formed so as to surround the MEMS structure 30, and a passivation in which an opening 29 is formed from above the wiring layer 27 to above the MEMS structure 30. A membrane 28 is provided.
A silicon oxide film 11 is formed on a p-type semiconductor substrate 10 made of silicon, and a silicon nitride film 12 is formed thereon. A MEMS structure 30 is provided on the silicon nitride film 12. The MEMS structure 30 is made of polysilicon and has a fixed electrode 20 and a movable electrode 26. The fixed electrode 20 is disposed on the silicon nitride film 12 and includes input side electrodes 21 a and 21 b and an output side electrode 22. The movable electrode 26 is held in the air in a both-sided state by holding portions rising from the input-side electrodes 21a and 21b.

One end of the input-side electrode 21 a extends to the wiring layer 27 surrounding the MEMS structure 30 and is connected to the wiring 31. In the wiring layer 27, an insulating film such as SiO ₂ is laminated, and the wiring 31 via the wiring layer 27 is connected to an aluminum wiring 32 from a connection pad provided on the wiring layer 27.
Further, one end of the output side electrode 22 extends to the wiring layer 27 surrounding the MEMS structure 30, is connected to the wiring 33, and is further connected to the aluminum wiring 34 from a connection pad provided on the wiring layer 27. .
An oxide film 24 such as SiO ₂ is formed under the wiring layer 27 and is a sacrificial layer when the MEMS structure 30 is released by etching.

  A p-type well 13 is formed in the semiconductor substrate 10 below the input-side electrodes 21 a and 21 b and the output-side electrode 22 that are fixed electrodes in the MEMS structure 30. The well 13 is formed in a region including the MEMS structure 30 in plan view.

  A passivation film 28 is formed continuously from above the wiring layer 27 to above the MEMS structure 30. An opening 29 is formed in the passivation film 28, and the MEMS layer 30 is released by etching the wiring layer 27 and the oxide film 24 from the opening 29, and the MEMS structure is formed between the passivation film 28 and the semiconductor substrate 10. A cavity 35 in which the body 30 is placed is defined. A fixed voltage is applied to the well 13.

In the MEMS device 1 having such a structure, when a DC voltage is applied to the movable electrode 26 via the input side electrode 21a of the MEMS structure 30, a potential difference is generated between the movable electrode 26 and the output side electrode 22, and the movable device 26 is movable. An electrostatic force acts between the electrode 26 and the output electrode 22. Here, when an AC voltage is further applied to the movable electrode 26, the electrostatic force increases or decreases, and the movable electrode 26 oscillates in a direction toward or away from the output-side electrode 22. At this time, charge movement occurs on the electrode surface of the output side electrode 22, and a current flows through the output side electrode 22. Since the vibration is repeated, a specific resonance frequency signal is output from the output-side electrode 22.
When the voltage applied to the MEMS structure 30 is equal to or lower than the inversion voltage of the well, the well 13 is used while being grounded.
On the other hand, when the voltage applied to the MEMS structure 30 is equal to or higher than the inversion voltage of the well, a voltage capable of maintaining a depletion state is applied to the well 13 for use.
For example, when the drive voltage of the MEMS structure 30 is 8 V and the potential at which the inversion layer is generated in the well 13 is 7 V, a potential difference between the well 13 and the MEMS structure 30 is applied by applying a voltage of 3 V to the well 13. 5V, and the well 13 of the semiconductor substrate 10 maintains a depletion state without generating an inversion layer. In this case, a well (n-type well) having a reverse polarity is formed around the well 13 as a guard ring (not shown), and the absolute value is equal to or higher than the voltage applied to the well 13 and has the same polarity as the well 13. The voltage of is applied and used. For example, when 3 V is applied to the well 13, 5 V is applied to the surrounding guard ring portion.

Next, a manufacturing method of the MEMS device having the above configuration will be described.
2, 3 and 4 are schematic partial cross-sectional views showing a method for manufacturing a MEMS device.
First, as shown in FIG. 2A, a silicon oxide film 11 is formed on a semiconductor substrate 10 made of silicon by thermal oxidation. Next, as shown in FIG. 2B, B ions are implanted into the semiconductor substrate 10 in a predetermined region to form a p-type well 13. Subsequently, a silicon nitride film 12 is formed on the silicon oxide film 11 as shown in FIG. Then, as shown in FIG. 2D, a polysilicon film is formed on the silicon nitride film 12, and input-side electrodes 21a and 21b and output-side electrodes 22 that are fixed electrodes 20 of the MEMS structure are formed by patterning. To do.

Next, as shown in FIG. 3A, an oxide film 24 such as SiO ₂ is formed on the input side electrodes 21 a and 21 b and the output side electrode 22. Thereafter, as shown in FIG. 3B, an opening hole 25 is formed in the oxide film 24 on the input side electrodes 21a and 21b. Subsequently, a polysilicon film is formed on the oxide film 24, patterned, and a movable electrode 26 of the MEMS structure is formed by etching as shown in FIG. Then, as shown in FIG. 3D, a wiring layer 27 in which wirings (not shown) are laminated through an insulating film such as SiO ₂ is formed.

Next, as shown in FIG. 4A, a passivation film 28 is formed on the wiring layer 27. Subsequently, as shown in FIG. 4B, an opening 29 is formed in the passivation film 28 above the MEMS structure.
Then, as shown in FIG. 4C, an acidic etching solution is contacted from the opening 29 to etch the wiring layer 27 and the oxide film 24 to release the MEMS structure 30. At this time, a cavity 35 is formed between the semiconductor substrate 10 and the passivation film 28. In this way, the MEMS device 1 as shown in FIG. 1 is manufactured.

As described above, in the MEMS device 1 of the present embodiment, the well 13 is formed below the fixed electrode 20 in the MEMS structure 30, and a positive voltage is applied to the fixed electrode 20 of the MEMS structure 30. It is composed of p-type wells. Further, a fixed voltage is applied to the well 13 so that the well 13 formed in the semiconductor substrate 10 below the fixed electrode 20 is depleted.
Thus, by forming a well 13 and applying a fixed voltage to the well 13 so that the well 13 is depleted, the surface of the semiconductor substrate 1 is depleted, and the apparent distance between the counter electrodes is increased by the depletion layer. Therefore, the parasitic capacitance in this part is reduced. Therefore, the parasitic capacitance between the MEMS structure 30 and the semiconductor substrate 10 can be reduced, high-frequency signal leakage through the surface of the semiconductor substrate 10 can be reduced, and the characteristics of the MEMS device 1 are stabilized.
(Modification 1)

Next, a modified example of the combination of the polarities of the semiconductor substrate and the well in the first embodiment will be described. In the first modification, the semiconductor substrate is a p-type substrate and the well is an n-type well. Further, circuit elements are formed on the semiconductor substrate, and the potential of the semiconductor substrate is set to a general 0V.
FIG. 5 is a partial schematic cross-sectional view showing the configuration of the MEMS device according to the first modification.
The MEMS device 5 includes a MEMS structure (here, the movable electrode of the MEMS structure is omitted and only the input electrode 131 of the fixed electrode is shown) on the semiconductor substrate 120, and a wiring layer 127 formed around the MEMS structure. And a passivation film 128 formed above the wiring layer 127.
A silicon oxide film 121 is formed on a p-type semiconductor substrate 120 made of silicon, and a silicon nitride film 122 is formed thereon. A MEMS structure is provided on the silicon nitride film 122. The MEMS structure has the same structure as the MEMS structure described with reference to FIG. 1, and detailed description thereof is omitted.

An n-type well 123 is formed in the semiconductor substrate 120 below the input-side electrode 131 that is a fixed electrode in the MEMS structure. The well 123 is formed in a region including the MEMS structure in plan view.
In addition, an electrode 125 is formed in a part of the well 123, and the electrode 125 is connected to the upper surface of the passivation film 128 through the wiring layer 127 by the wiring 126.
A positive voltage is applied to the well 123 via the wiring 126. Further, a negative voltage is applied to the input side electrode 131 of the MEMS structure.

Here, a threshold voltage at which an inversion layer is generated in the well 123 is Vth, a bias voltage applied to the MEMS structure is Vp, and a voltage applied to the well 123 below the MEMS structure is Vwell.
FIG. 6 is a graph showing the relationship between the difference between Vp and Vwell (Vp−Vwell) and the capacitance C between the MEMS structure and the well in such a state.
When the semiconductor substrate 120 is a p-type substrate and the well 123 is an n-type well, the threshold voltage Vth <0. When the voltage of Vp−Vwell is positive, the well is in an accumulation state, and the capacitance C between the MEMS structure and the well is a large value and the parasitic capacitance is large. The range of Vp−Vwell between 0 and the threshold voltage Vth is a range in which the well is depleted, and the capacitance C between the MEMS structure and the well decreases from 0 V toward the threshold voltage Vth and becomes parasitic. The capacity is also reduced. When the threshold voltage Vth is decreased, the well is inverted. As described above, by using the well in a depleted state, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and signal leakage in the lateral direction can hardly occur near the substrate surface. .
In order to make this well depleted, it is necessary to satisfy the conditions of Vp <0, Vwell ≧ 0, and 0 <| Vp−Vwell | <| Vth |.

As described above, when the above conditions are satisfied, when the semiconductor substrate 120 is a p-type substrate and the well 123 is an n-type well, the well 123 formed in the semiconductor substrate 120 below the fixed electrode is depleted. Become. Then, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well 123, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate 120 can be reduced, high-frequency signals are not leaked through the surface of the semiconductor substrate 120, and the characteristics of the MEMS device 5 can be stabilized. it can. And if such a structure is employ | adopted, it will become easy to integrate and utilize circuits, such as a MEMS structure and IC.
(Modification 2)

Next, another modification example according to the combination of the polarities of the semiconductor substrate and the well in the first embodiment will be described. In the second modification, the semiconductor substrate is an n-type substrate and the well is a p-type well. Further, circuit elements are formed on the semiconductor substrate, and the potential of the semiconductor substrate is set to a general 0V.
FIG. 7 is a partial schematic cross-sectional view showing the configuration of the MEMS device in Modification 2.
The MEMS device 6 includes a MEMS structure on the semiconductor substrate 140 (here, the movable electrode of the MEMS structure is omitted and only the input electrode 151 of the fixed electrode is shown), and a wiring layer 147 formed around the MEMS structure. And a passivation film 148 formed above the wiring layer 147.
A silicon oxide film 141 is formed on an n-type semiconductor substrate 140 made of silicon, and a silicon nitride film 142 is formed thereon. A MEMS structure is provided on the silicon nitride film 142. The MEMS structure has the same structure as the MEMS structure described with reference to FIG. 1, and detailed description thereof is omitted.

A p-type well 143 is formed in the semiconductor substrate 140 below the input-side electrode 151 that is a fixed electrode in the MEMS structure. The well 143 is formed in a region including the MEMS structure in a plan view.
An electrode 145 is formed in part of the well 143, and the electrode 145 is connected to the upper surface of the passivation film 148 through the wiring layer 147 by the wiring 146.
A negative voltage is applied to the well 143 through the wiring 146. A positive voltage is applied to the input side electrode 151 of the MEMS structure.

Here, the threshold voltage at which the inversion layer is generated in the well 143 is Vth, the bias voltage applied to the MEMS structure is Vp, and the voltage applied to the well 143 below the MEMS structure is Vwell.
FIG. 8 is a graph showing the relationship between the difference between Vp and Vwell (Vp−Vwell) and the capacitance C between the MEMS structure and the well in such a state.
When the semiconductor substrate 140 is an n-type substrate and the well 143 is a p-type well, the threshold voltage Vth> 0. When the voltage of Vp−Vwell is negative, the well is in an accumulation state, and the capacitance C between the MEMS structure and the well is a large value and the parasitic capacitance is large. The range of Vp−Vwell between 0 and the threshold voltage Vth is a range in which the well is depleted, and the capacitance C between the MEMS structure and the well decreases from 0 V toward the threshold voltage Vth and becomes parasitic. The capacity is also reduced. When the voltage exceeds the threshold voltage Vth, the well is inverted. As described above, by using the well in a depleted state, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and signal leakage in the lateral direction can hardly occur near the substrate surface. .
In order to make this well depleted, it is necessary to satisfy the conditions of Vp> 0, Vwell ≦ 0, and 0 <| Vp−Vwell | <| Vth |.

As described above, by satisfying the above conditions, when the semiconductor substrate 140 is an n-type substrate and the well 143 is a p-type well, the well 143 formed in the semiconductor substrate 140 below the fixed electrode is depleted. Become. Then, the apparent distance between the counter electrodes is increased by the depletion layer generated in the well 143, so that the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate 140 can be reduced, and high-frequency signals can be prevented from leaking through the surface of the semiconductor substrate 140, and the characteristics of the MEMS device 6 can be stabilized. it can. And if such a structure is employ | adopted, it will become easy to integrate and utilize circuits, such as a MEMS structure and IC.
(Second Embodiment)

Next, a MEMS device according to the second embodiment will be described.
The present embodiment is different from the first embodiment in that wells formed in the semiconductor substrate are provided independently for the input side electrode and the output side electrode, respectively.
FIG. 9 shows the configuration of the MEMS device of the present embodiment, FIG. 9A is a partial schematic plan view of the MEMS device, and FIG. 9B is a partial schematic cross-sectional view taken along the line BB in FIG. It is.

The MEMS device 2 includes a MEMS structure 60 in the semiconductor substrate 10, a wiring layer 57 formed so as to surround the MEMS structure 60, and a passivation in which an opening 59 is formed from above the wiring layer 57 to above the MEMS structure 60. A membrane 58 is provided.
A silicon oxide film 11 is formed on a p-type semiconductor substrate 10 made of silicon, and a silicon nitride film 12 is formed thereon. A MEMS structure 60 is provided on the silicon nitride film 12. The MEMS structure 60 is made of polysilicon and has a fixed electrode 50 and a movable electrode 56. The fixed electrode 50 is disposed on the silicon nitride film 12 and includes input side electrodes 51 a and 51 b and an output side electrode 52. The movable electrode 56 is held in the air in the both-sided state by holding the portions rising from the input-side electrodes 51a and 51b.

One end of the input side electrode 51 a extends to the wiring layer 57 surrounding the MEMS structure 60 and is connected to the wiring 61. The wiring layer 57 is laminated with an insulating film such as SiO _2, and the wiring 61 passing through the wiring layer 57 is connected to the aluminum wiring 62 from a connection pad provided on the wiring layer 57.
Further, one end of the output side electrode 52 extends to the wiring layer 57 and is connected to the wiring 63, and is further connected to the aluminum wiring 64 from a connection pad provided on the upper part of the wiring layer 57.
An oxide film 54 such as SiO ₂ is formed under the wiring layer 57, and is a sacrificial layer when the MEMS structure 60 is released by etching.

In addition, p-type wells 43a and 43b are formed in the semiconductor substrate 10 below the input-side electrodes 51a and 51b, which are the fixed electrodes 50 in the MEMS structure 60, respectively.
A passivation film 58 is formed continuously from above the wiring layer 57 and above the MEMS structure 60. An opening 59 is formed in the passivation film 58, and the MEMS structure 60 is released by etching the wiring layer 57 and the oxide film 54 from the opening 59, and the MEMS structure is interposed between the passivation film 58 and the semiconductor substrate 10. A cavity 65 in which the body 60 is placed is defined. A fixed voltage is applied to each of the wells 43a and 43b.

In the MEMS device 2 having such a structure, when a DC voltage is applied to the movable electrode 56 via the input side electrode 51a of the MEMS structure 60, a potential difference is generated between the movable electrode 56 and the output side electrode 52. An electrostatic force acts between the electrode 56 and the output side electrode 52. Here, when an AC voltage is further applied to the movable electrode 56, the electrostatic force increases or decreases, and the movable electrode 56 vibrates in a direction in which the movable electrode 56 approaches or moves away from the output-side electrode 52. At this time, charge movement occurs on the electrode surface of the output side electrode 52, and a current flows through the output side electrode 52. Since the vibration is repeated, a specific resonance frequency signal is output from the output side electrode 52.
When the voltage applied to the MEMS structure 60 is equal to or lower than the inversion voltage of the well, the wells 43a and 43b are used while being grounded.
On the other hand, when the voltage applied to the MEMS structure 60 is equal to or higher than the inversion voltage of the well, a voltage capable of maintaining a depletion state is applied to the well 43a and the well 43b.
For example, when the drive voltage of the MEMS structure 60 is 8V and the potential at which the inversion layer is generated in the semiconductor substrate 10 is 7V, a voltage of 3V is applied to the wells 43a and 43b, so that the semiconductor substrate 10 and the MEMS structure 60 The potential difference between them is 5V, and the wells 43a and 43b of the semiconductor substrate 10 are maintained in a depleted state without the occurrence of inversion layers.
In this case, a well having the opposite polarity is formed as a guard ring around the wells 43a and 43b (not shown), and an absolute value equal to or higher than that of the well 13 is applied to the wells 43a and 43b. To use. For example, when 3V is applied to the wells 43a and 43b, 5V is applied to the surrounding guard ring portions.

Next, a method for manufacturing the MEMS vibrator having the above configuration will be described.
10, FIG. 11 and FIG. 12 are schematic partial cross-sectional views showing a method for manufacturing a MEMS device.
First, as shown in FIG. 10A, a silicon oxide film 11 is formed on a semiconductor substrate 10 made of silicon by thermal oxidation. Next, as shown in FIG. 10B, p-type wells 43a and 43b are formed by implanting B ions into the semiconductor substrate 10 in a predetermined region. Subsequently, a silicon nitride film 12 is formed on the silicon oxide film 11 as shown in FIG. Then, as shown in FIG. 10 (d), a polysilicon film is formed on the silicon nitride film 12, and input-side electrodes 51a and 51b and output-side electrodes 52 that are fixed electrodes 50 of the MEMS structure are formed by patterning. To do.

Next, as shown in FIG. 11A, an oxide film 54 such as SiO ₂ is formed on the input side electrodes 51 a and 51 b and the output side electrode 52. Thereafter, as shown in FIG. 11B, an opening hole 55 is formed in the oxide film 54 on the input side electrodes 51a and 51b. Subsequently, a polysilicon film is formed on the oxide film 54, patterned, and a movable electrode 56 of the MEMS structure is formed by etching as shown in FIG. Then, as shown in FIG. 11D, a wiring layer 57 in which wirings (not shown) are laminated through an insulating film such as SiO ₂ is formed.

Next, as shown in FIG. 12A, a passivation film 58 is formed on the wiring layer 57. Subsequently, as shown in FIG. 12B, an opening 59 is formed in the passivation film 58 above the MEMS structure.
Then, as shown in FIG. 12C, an acidic etching solution is contacted from the opening 59 to etch the wiring layer 57 and the oxide film 54 to release the MEMS structure 60. At this time, a cavity 65 is formed between the semiconductor substrate 10 and the passivation film 58. In this way, the MEMS device 2 as shown in FIG. 9 is manufactured.

As described above, in the MEMS device 2 of the present embodiment, the wells 43a and 43b are formed below the fixed electrode 50 in the MEMS structure 60, and a positive voltage is applied to the fixed electrode 50 of the MEMS structure 60. 43a and 43b are p-type wells. Further, a fixed voltage is applied to the wells 43a and 43b so that the wells 43a and 43b formed in the semiconductor substrate 10 below the fixed electrode 50 are depleted.
In this way, the wells 43a and 43b are formed and a fixed voltage is applied to the wells 43a and 43b so that the wells 43a and 43b are depleted, so that the surface of the semiconductor substrate 10 is depleted, and the depletion layer has an apparent appearance. Since the distance between the counter electrodes increases, the parasitic capacitance in this portion decreases. Therefore, the parasitic capacitance between the MEMS structure 60 and the semiconductor substrate 10 can be reduced, high-frequency signal leakage can be reduced through the surface of the semiconductor substrate 10, and the characteristics of the MEMS device 2 are stabilized. be able to.
Moreover, in this embodiment, since the board | substrate structure below each of the input side electrode and output side electrode of a MEMS part is independent, it can reduce from the signal leakage of a board | substrate horizontal direction. As a result, the insulation between the input-side electrodes 51a and 51b and the output-side electrode 52 can be further improved, and the characteristics of the MEMS device 2 can be stabilized.
(Third embodiment)

Next, a MEMS device according to the third embodiment will be described.
The present embodiment is different from the first and second embodiments in the structure of a well formed in a semiconductor substrate. The configuration of the MEMS structure is the same as that of the second embodiment.
FIG. 13 shows the configuration of the MEMS device of the present embodiment, FIG. 13A is a partial schematic plan view of the MEMS device, and FIG. 13B is a partial schematic cross-sectional view taken along the line CC in FIG. It is. In these drawings, the wiring layer surrounding the MEMS structure described in the above embodiment is omitted, and only characteristic portions are schematically shown.

The MEMS device 3 includes a MEMS structure 90 including a fixed electrode 80 and a movable electrode 86 on a semiconductor substrate 10.
A silicon oxide film 11 is formed on a p-type semiconductor substrate 10 made of silicon, and a silicon nitride film 12 is formed thereon. A MEMS structure 90 is provided on the silicon nitride film 12. The MEMS structure 90 is made of polysilicon and has a fixed electrode 80 and a movable electrode 86. The fixed electrode 80 is disposed on the silicon nitride film 12 and includes an input side electrode 81, a drive electrode 82, and an output side electrode 83. The movable electrode 86 is held in the air in a cantilevered state by holding the portion rising from the input side electrode 81.

A p-type well 70 having the same polarity as that of the semiconductor substrate 10 is formed on the semiconductor substrate 10 below the input electrode 81, the drive electrode 82, and the output electrode 83 that are the fixed electrodes 80 in the MEMS structure 90. Further, an n-type separation well 71 having a polarity opposite to that of the well 70 is formed so as to surround the well 70. The well 70 and the separation well 71 are formed in a region including the MEMS structure 90 in plan view.
Note that a fixed voltage Vwp is applied to the well 70 and a fixed voltage Vwn is applied to the separation well, and the relationship of Vwp <Vwn is set.
At this time, the voltage applied to the well 70 is a voltage that can maintain the depletion state of the well 70. For example, when the driving voltage of the MEMS structure 90 is 10 V and the potential at which the inversion layer is generated in the semiconductor substrate 10 is 7 V, a voltage of Vwp = 5 V is applied to the well 70, so that the well 70 and the MEMS structure 90 The potential difference between them is 5 V, and the well 70 of the semiconductor substrate 10 is maintained in a depleted state without generating an inversion layer. A voltage of Vwn = 6V is applied to the separation well 71, and a voltage is applied so that a reverse bias is applied between the adjacent n-type well and p-type well.

As described above, in the MEMS device 3 of this embodiment, the well 70 is formed below the fixed electrode 80 in the MEMS structure 90, and a positive voltage is applied to the fixed electrode 80 of the MEMS structure 90. It is composed of p-type wells. Further, a fixed voltage is applied to the well 70 so that the well 70 formed in the semiconductor substrate 10 below the fixed electrode 80 is depleted.
In this way, the surface of the well 70 is depleted, and the apparent distance between the counter electrodes is increased by the depletion layer, so that the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure 90 and the semiconductor substrate 10 can be reduced, high-frequency signals are not leaked through the surface of the semiconductor substrate 10, and the characteristics of the MEMS device 3 are stabilized. Can do.
In addition, a separation well 71 surrounding the well 70 is formed, and the voltage applied to the separation well 71 is higher than the voltage applied to the well 70.
In this way, when the movable electrode 86 of the MEMS structure 90 is operated at a higher voltage, current does not flow from the well 70 to the separation well 71, and the portion where the MEMS structure 90 is formed is prevented. The potential can be separated from the others. And if such a structure is employ | adopted, it will become easy to provide the device which integrated the MEMS structure 90 and circuits, such as IC.
(Modification 3)

Next, a modified example in the third embodiment will be described. In the third modification, the semiconductor substrate is a p-type substrate, the well is a p-type well, and the separation well is an n-type well, and no voltage is applied to the separation well. Further, circuit elements are formed on the semiconductor substrate, and the potential of the semiconductor substrate is set to a general 0V.
FIG. 14 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 3.
The MEMS device 7 includes a MEMS structure on a semiconductor substrate 160 (here, the movable electrode of the MEMS structure is omitted and only the input electrode 171 of the fixed electrode is shown), and a wiring layer 167 formed around the MEMS structure. And a passivation film 168 formed above the wiring layer 167.
A silicon oxide film 161 is formed on a p-type semiconductor substrate 160 made of silicon, and a silicon nitride film 162 is formed thereon. A MEMS structure is provided on the silicon nitride film 162. The MEMS structure has the same structure as the MEMS structure described with reference to FIG. 1, and detailed description thereof is omitted.

A p-type well 163 having the same polarity as the semiconductor substrate 160 is formed in the semiconductor substrate 160 below the input side electrode 171 in the MEMS structure. The well 163 is formed in a region including the MEMS structure in plan view. Further, an n-type separation well 164 having a polarity opposite to that of the well 163 is formed in the semiconductor substrate 160 so as to surround the well 163. A positive voltage is applied to the input side electrode 171 of the MEMS structure.
An electrode 165 is formed in part of the well 163, and the electrode 165 is connected to the upper surface of the passivation film 168 through the wiring layer 167 by the wiring 166. By applying a positive or negative voltage to the electrode 165, the separation well 164 and the semiconductor substrate 160 are in a reverse bias state.

Here, it is assumed that the threshold voltage at which the inversion layer is generated in the well 163 is Vth, the bias voltage applied to the MEMS structure is Vp, and the voltage applied to the well 163 below the MEMS structure is Vwell.
The relationship between the difference between Vp and Vwell (Vp−Vwell) in this state and the capacitance C between the MEMS structure and the well is the same as the graph shown in FIG.
Therefore, when the semiconductor substrate 160 is a p-type substrate, the well 163 is a p-type well, and the separation well 164 is an n-well, the threshold voltage Vth> 0.
When the voltage of Vp−Vwell is negative, the well is in an accumulation state, and the capacitance C between the MEMS structure and the well is a large value and the parasitic capacitance is large. The range of Vp−Vwell between 0 and the threshold voltage Vth is a range in which the well is depleted, and the capacitance C between the MEMS structure and the well decreases from 0 V toward the threshold voltage Vth and becomes parasitic. The capacity is also reduced. When the voltage exceeds the threshold voltage Vth, the well is inverted. As described above, by using the well in a depleted state, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and signal leakage in the lateral direction can hardly occur near the substrate surface. .
In order to make this well depleted, it is necessary to satisfy the conditions of Vp> 0 and 0 <Vp−Vwell <Vth. In this case, Vwell may be a positive voltage or a negative voltage as long as it satisfies the above conditions.

As described above, by satisfying the above-described conditions, when the semiconductor substrate 160 is a p-type substrate, the well 163 is a p-type well, and the separation well 164 is an n-type well, the semiconductor substrate 160 below the fixed electrode is formed. The formed well 163 is depleted. Then, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well 163, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate 160 can be reduced, and high-frequency signals can be prevented from leaking through the surface of the semiconductor substrate 160, and the characteristics of the MEMS device 7 can be stabilized. it can. If such a configuration is adopted, the potential of the well does not affect the potential of the semiconductor substrate, so that the MEMS structure and a circuit such as an IC can be used in an integrated manner.
(Modification 4)

Next, another modification example according to the combination of the polarities of the semiconductor substrate and the well in the third embodiment will be described. In the fourth modification, the semiconductor substrate is an n-type substrate, the well is an n-type well, and the separation well is a p-type. Further, circuit elements are formed on the semiconductor substrate, and the potential of the semiconductor substrate is set to a general 0V.
FIG. 15 is a partial schematic cross-sectional view showing a configuration of a MEMS device according to Modification 4.
The MEMS device 8 includes a MEMS structure on the semiconductor substrate 180 (here, the movable electrode of the MEMS structure is omitted and only the input electrode 191 of the fixed electrode is shown), and a wiring layer 187 formed around the MEMS structure. And a passivation film 188 formed above the wiring layer 187.
A silicon oxide film 181 is formed on an n-type semiconductor substrate 180 made of silicon, and a silicon nitride film 182 is formed thereon. A MEMS structure is provided on the silicon nitride film 182. The MEMS structure has the same structure as the MEMS structure described with reference to FIG. 1, and detailed description thereof is omitted.

An n-type well 183 having the same polarity as the semiconductor substrate 180 is formed in the semiconductor substrate 180 below the input side electrode 191 in the MEMS structure. The well 183 is formed in a region including the MEMS structure in plan view. Further, a p-type separation well 184 having a polarity opposite to that of the well 183 is formed in the semiconductor substrate 180 so as to surround the well 183. A negative voltage is applied to the input side electrode 191 of the MEMS structure.
An electrode 185 is formed in a part of the well 183, and the electrode 185 is connected to the upper surface of the passivation film 188 through a wiring layer 187 by a wiring 186. By applying a negative or positive voltage to the electrode 185, the separation well 184 and the semiconductor substrate 180 are in a reverse bias state.

Here, the threshold voltage at which the inversion layer is generated in the well 183 is Vth, the bias voltage applied to the MEMS structure is Vp, and the voltage applied to the well 183 below the MEMS structure is Vwell.
The relationship between the difference between Vp and Vwell (Vp−Vwell) in this state and the capacitance C between the MEMS structure and the well is the same as the graph shown in FIG.
When the semiconductor substrate 180 is an n-type substrate, the well 183 is an n-type well, and the separation well 184 is a p-type well, the threshold voltage Vth <0.
When the voltage of Vp−Vwell is positive, the well is in an accumulation state, and the capacitance C between the MEMS structure and the well is a large value and the parasitic capacitance is large. The range of Vp−Vwell between 0 and the threshold voltage Vth is a range in which the well is depleted, and the capacitance C between the MEMS structure and the well decreases from 0 V toward the threshold voltage Vth and becomes parasitic. The capacity is also reduced. When the threshold voltage Vth is decreased, the well is inverted. As described above, by using the well in a depleted state, the parasitic capacitance between the MEMS structure and the semiconductor substrate can be reduced, and signal leakage in the lateral direction can hardly occur near the substrate surface. .
In order to make this well depleted, it is necessary to satisfy the conditions of Vp <0 and 0 <Vp−Vwell <Vth. In this case, Vwell may be a positive voltage or a negative voltage as long as it satisfies the above conditions.

  As described above, by satisfying the above conditions, when the semiconductor substrate 180 is an n-type substrate, the well 183 is an n-type well, and the separation well 184 is a p-type well, the semiconductor substrate 180 below the fixed electrode is formed. The formed well 183 is depleted. Then, since the apparent distance between the counter electrodes is increased by the depletion layer generated in the well 183, the parasitic capacitance in this portion is reduced. Therefore, the parasitic capacitance between the MEMS structure and the semiconductor substrate 180 can be reduced, high-frequency signals are not leaked through the surface of the semiconductor substrate 180, and the characteristics of the MEMS device 8 can be stabilized. it can. If such a configuration is adopted, the potential of the well does not affect the potential of the semiconductor substrate, so that the MEMS structure and a circuit such as an IC can be used in an integrated manner.

  1, 2, 3, 5, 6, 7, 8 ... MEMS device, 10 ... Semiconductor substrate, 11 ... Silicon oxide film, 12 ... Silicon nitride film, 13 ... Well, 20 ... Fixed electrode, 21a, 21b ... Input side electrode , 22 ... output side electrode, 24 ... oxide film, 26 ... movable electrode, 27 ... wiring layer, 28 ... passivation film, 29 ... opening, 30 ... MEMS structure, 31 ... wiring, 32 ... aluminum wiring, 33 ... wiring 34 ... Aluminum wiring, 35 ... Cavity, 43a, 43b ... Well, 50 ... Fixed electrode, 51a, 51b ... Input side electrode, 52 ... Output side electrode, 54 ... Oxide film, 56 ... Moving electrode, 57 ... Wiring layer 58 ... Passivation film, 59 ... Opening, 60 ... MEMS structure, 61 ... Wiring, 62 ... Aluminum wiring, 63 ... Wiring, 64 ... Aluminum wiring, 65 ... Cavity, 70 ... Well, 71 ... Separation well, 8 DESCRIPTION OF SYMBOLS ... Fixed electrode, 81 ... Input side electrode, 82 ... Drive electrode, 83 ... Output side electrode, 86 ... Movable electrode, 90 ... MEMS structure, 120 ... Semiconductor substrate, 123 ... Well, 131 ... Input side electrode, 140 ... Semiconductor Substrate, 143... Well, 151... Input side electrode.

Claims (7)

A MEMS device comprising a MEMS structure having a fixed electrode and a movable electrode formed on a semiconductor substrate via an insulating layer,
A well is formed in the semiconductor substrate below the fixed electrode. When a positive voltage is applied to the fixed electrode, the well is a p-type well, and a negative voltage is applied to the fixed electrode. A MEMS device, wherein the well is an n-type well. The MEMS device according to claim 1, wherein
A MEMS device, wherein a voltage is applied to the well so that the well is depleted. The MEMS device according to claim 2, wherein
The semiconductor substrate is a p-type substrate and the well is an n-type well;
When the bias voltage of the MEMS structure is Vp, the voltage applied to the well below the MEMS structure is Vwell, and the threshold voltage at which an inversion layer is generated in the well is Vth,
A MEMS device characterized by satisfying Vp <0, Vwell ≧ 0, and 0 <| Vp−Vwell | <| Vth |. The MEMS device according to claim 2, wherein
The semiconductor substrate is an n-type substrate and the well is a p-type well;
When the bias voltage of the MEMS structure is Vp, the voltage applied to the well below the MEMS structure is Vwell, and the threshold voltage at which an inversion layer is generated in the well is Vth,
A MEMS device characterized by satisfying Vp> 0, Vwell ≦ 0, and 0 <| Vp−Vwell | <| Vth |. A MEMS device comprising a MEMS structure having a fixed electrode and a movable electrode formed on a semiconductor substrate via an insulating layer,
A well having the same polarity as the semiconductor substrate is formed in the semiconductor substrate below the fixed electrode;
Surrounding the well in the semiconductor substrate, a separation well having a polarity opposite to the well is formed;
A MEMS device configured to have a reverse bias between the well and the separation well or between the separation well and the semiconductor substrate. The MEMS device according to claim 5, wherein
The semiconductor substrate is a p-type substrate, the well is a p-type well, and the separation well is an n-type well,
When the bias voltage of the MEMS structure is Vp, the voltage applied to the well below the MEMS structure is Vwell, and the threshold voltage at which an inversion layer is generated in the well is Vth,
A MEMS device characterized by satisfying Vp> 0 and 0 <Vp−Vwell <Vth. The MEMS device according to claim 5, wherein
The semiconductor substrate is an n-type substrate, the well is an n-type well, and the separation well is a p-type well,
When the bias voltage of the MEMS structure is Vp, the voltage applied to the well below the MEMS structure is Vwell, and the threshold voltage at which an inversion layer is generated in the well is Vth,
A MEMS device characterized by satisfying Vp <0 and 0 <Vp−Vwell <Vth.

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