JP4621257B2 - Variable inductor type MEMS pressure sensor using magnetostrictive effect - Google Patents

Description

  The present invention relates to a pressure sensor. More specifically, the present invention relates to a variable inductance type pressure sensor that uses a magnetostrictive effect in which a magnetic permeability is greatly changed by a pressure acting externally with a magnetostrictive substance as a core, and is a MEMS (Micro Electro Mechanical System). ) It relates to a pressure sensor formed using technology.

  The semiconductor pressure sensor is a pressure sensor that has recently been put into practical use, and there is no phenomenon that the characteristic curve when pressure is applied differs from the characteristic curve when pressure is reduced from a pressurized state, that is, there is no hysteresis phenomenon. In addition, because it is excellent in linearity and small and light, it is characterized by being extremely resistant to vibration. Moreover, the semiconductor pressure sensor is more sensitive and reliable than the mechanical type, and is excellent in mass productivity.

  The micro pressure sensor using MEMS process technology includes a piezoresistive sensor using the piezoresistive effect, a capacitive sensor that measures the change in capacitance due to the behavior of the thin film due to pressurization, and a change in the resonant frequency of the beam. A vibration type sensor to measure is typical.

  The piezoresistive pressure sensor detects the amount of change in the resistance component through a signal detection unit after sensing the amount of change in the resistance component using a diffusion resistor configured in a bridge configuration on the diaphragm of the silicon wafer. A sensor whose pressure is measured. Such a piezoresistive pressure sensor is the most commonly used sensor, but due to the sensitivity of the piezo material with temperature, additional circuit configuration is required, such as the Wheatstone bridge method at the time of sensor fabrication. And it is not easy for telemetry.

  The capacitance type pressure sensor detects the stress by converting this change into an electric signal when the distance between the electrode plates facing each other changes due to external stress and the capacitance between the electrodes changes. It is a sensor. Such a capacitive pressure sensor is less sensitive to temperature, can be manufactured with MEMS technology, and works even with low pressure changes, so it is often used where precision measurement is required. The FOM (Figure Of Merit) representing the sensitivity of the sensor is small, the operating region (Span region) is a narrow band, and the manufacturing process is not easier than a piezoresistive sensor.

  In addition, when using a piezoresistive type or a capacitance type pressure sensor in a high frequency (UHF band or higher) band, the influence of the resistance component and the high frequency parasitic component of the semiconductor (Si series) increases as the frequency increases. There must be devised special structures or materials / structures that can be used in a special high frequency band, and there are few high frequency pressure sensors that are currently available for use.

  The method of measuring the pressure using the change in inductance has been advanced for the last ten years, but has been developed as an application related to the RF tag rather than the result for the sensor itself. Is too large to apply to a microsensor, or even if it can be fabricated with a MEMS structure, it has to be very difficult to perform, so it is not practical.

  An object of the present invention to solve the above problem is to provide an inductor type pressure sensor that is suitable for high-frequency applications and is compatible with a MEMS process, has high FOM (sensor sensitivity), and enables precise measurement. Is to provide.

  In order to achieve the above object, a variable inductor type MEMS pressure sensor using a magnetostrictive effect according to the present invention has a coil portion in which a plurality of annular electrodes are connected in series on a first substrate, and is constant with the first substrate. A magnetostrictive thin film corresponding to the annular electrode is formed on a second substrate facing in parallel at a distance, and the coil portion and the magnetostrictive thin film constitute an inductor, and the magnetostrictive thin film is formed by an external pressure. An inductor array unit that induces a change in permeability to change the inductance of the coil unit, and the inductor array unit and the LC resonance circuit constitute magnetic energy discharged in the inductor array unit in voltage form And a capacitor unit that stores the converted data.

  The variable inductor type MEMS pressure sensor using the magnetostrictive effect of the present invention is more sensitive than the existing piezoresistive type or capacitance type sensor, so that the resolution is excellent and the MEMS is compatible with a semiconductor process. Since it is manufactured using process technology, it is possible to reduce the production cost because it can be miniaturized and mass-processed. In addition, the pressure sensor of the present invention can be used as a human body insertion type or a real-time state diagnosis system because it can create a non-power / wireless sensor that does not require a power source and can measure pressure in a non-power state.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a plan view showing a configuration of a variable inductor type MEMS pressure sensor using a magnetostriction effect according to the present invention.

  The variable inductor type MEMS pressure sensor using the magnetostrictive effect of the present invention includes an inductor array unit 100 and a capacitor unit 200 that constitute an LC resonance circuit.

  The inductor array unit 100 induces deformation of the magnetostrictive material thin film by pressure applied from the outside, and changes the inductance of the sensor by changing the magnetic permeability of the magnetostrictive material thin film. The inductor array unit 100 has a coil-like annular shape on a plurality of coil-like annular electrodes 110 formed so as to be connected in series on a glass substrate and a dielectric thin film facing the glass substrate in parallel at a constant interval. A plurality of magnetostrictive material thin films 120 formed at the center of the annular electrode 110 so as to have a one-to-one correspondence with the electrode 110 includes a plurality of unit cells 130 that form a pair. That is, in order to implement a solenoid having a magnetostrictive material as a core using the MEMS process technology, the inductor array unit 100 is formed by forming a plurality of annular electrodes on the same substrate and then electrically connecting them in series. To form a coil portion of the inductor. Then, by forming the magnetostrictive material thin film 120 so as to correspond to the central portion of each annular electrode 110, a circuit equivalent to an inductor network in which a plurality of solenoids having a magnetostrictive material as a core are connected in series as shown in FIG. Configure. At this time, amorphous and single crystal alloys are used as the magnetostrictive material.

  The capacitor unit 200 stores the magnetic energy discharged in the inductor array unit 100 by converting it into a voltage form, and is connected to the annular electrodes at both ends of the annular electrodes 110 connected in series in the inductor array unit 100. Thus, an LC tank (TANK) circuit (LC resonance circuit) is formed together with the inductor array unit 100.

  The energy change generated in the coil portion (primary side coil) of the inductor array unit 100 due to the external pressure is transmitted to the inductor (secondary side coil) of the external measuring device (not shown) by the mutual inductance action, and externally. By calculating a change in inductance measured through a secondary coil with a measuring device (not shown), it is possible to perform remote measurement without power supply / wireless with respect to the pressure applied to the inductor array unit 100.

  FIG. 3 is a cross-sectional view of the sensor of FIG. 1 cut in the A-A ′ direction, and shows the configuration of the inductor array unit 100 in more detail.

  In the inductor array unit 100, a lower substrate 140 and an upper substrate 150 are formed in parallel within a housing 400 at a predetermined interval, and an annular electrode 110 is formed on the upper surface of the lower substrate 140 facing the upper substrate 150. It is formed. At this time, the annular electrode 110 is made of gold (Au) or copper (Cu) and is formed through electroplating or other thick film metal forming process. As the lower substrate 140, Pyrex (registered trademark) or quartz glass is used.

  A support substrate 170 is formed on the lower surface of the lower substrate 140 to absorb external vibrations and adhere the sensor to the housing 400. Such a support substrate 170 is formed of a soft polymer.

  A magnetostrictive material thin film 120 is formed on the lower surface of the upper substrate 150 facing the upper surface of the lower substrate 140 so as to have a one-to-one correspondence with each annular electrode 110 to form a unit cell 130. The magnetostrictive material thin film 120 is an inductor core for each unit cell 130 of the inductor array unit 100, and an amorphous magnetostrictive material or a magnetostrictive material in the form of a single crystal alloy is formed on the upper substrate 150 by a metal film deposition technique. A thin film is formed on the lower surface of the film.

  A pressure introducing groove 180 is formed on the upper surface of the upper substrate 150 so as to have a one-to-one correspondence with the magnetostrictive material thin film 120 in order to easily transmit externally applied pressure to the magnetostrictive material thin film 120. As such an upper substrate 150, a dielectric thin film is used.

  In order to prevent the annular electrode 110 of the lower substrate 140 from contacting the magnetostrictive material thin film 120 of the upper substrate 150 when the dielectric thin film is deformed by pressure applied from the outside, the lower substrate 140 and the upper substrate 150 are: The spacer 160 is maintained so as to be separated by a certain distance. The space formed by the spacer 160 also serves as a reference pressure chamber. The spacer 160 is formed of a material such as silicon.

  The upper surface of the sensor to which an external pressure is applied is formed with a diaphragm 300 made of silicon rubber for blocking direct contact with an external substance, and protects other surfaces excluding the upper surface of the sensor. A housing 400 for fixing the diaphragm 300 is formed so as to cover the side surfaces of the lower substrate 140 and the upper substrate 150.

  4 to 11 are cross-sectional views showing a manufacturing process of the inductor array unit 100 of FIG. 3, and show a manufacturing process for one unit cell.

First, a silicon etch mask such as SiO ₂ or Si ₃ Nx is grown or deposited on a silicon wafer to a thickness sufficient to serve as an etch mask, and then a pressure introducing groove 180 is formed as shown in FIG. The upper substrate 150 is formed by performing wet etching so that the region to be formed is a diagram having a thickness of about t.

  Next, after the magnetostrictive material is vacuum-deposited on the lower surface (upper surface in FIG. 5) of the upper substrate 150 corresponding to the pressure introducing groove 180, the deposited magnetostrictive material thin film is etched to form on the upper substrate 150 as shown in FIG. A magnetostrictive material thin film 120 is formed.

  Next, a metal seed layer 142 is deposited on Pyrex (registered trademark) or quartz glass 140 separately from the upper substrate 150 on which the magnetostrictive material thin film 120 is formed, and then a thick film is formed on the metal seed layer 142. Photoresist (PR) 144 is patterned into a coil. Then, after gold (Au) or copper (Cu) is electroplated according to the patterned form to form the annular electrode 110, the thick film PR 144 is removed as shown in FIG.

Next, the remaining portion of the metal seed layer 142 excluding the portion between the annular electrode 110 and the glass substrate 140 is etched as shown in FIG. At this time, the selectivity between the annular electrode 110 and the metal seed layer 142 is ER _coil : ER _seed = 1: 10 or more with respect to the metal seed etching solution. Here, ER represents the etching rate.

  Next, as shown in FIG. 9, a spacer 160 formed of silicon is formed on the glass substrate 140 through anodic bonding.

  Next, the upper substrate 150 of FIG. 5 is bonded to the other surface of the spacer 160 so that the magnetostrictive material thin film 120 corresponds to the center of the annular electrode 110 as shown in FIG. At this time, melt bonding, eutectic bonding, organic bonding, or the like can be used as a bonding method.

  Next, after the inner bottom surface of the housing 400 formed by injection molding is applied with the epoxy 170, the sensor is placed on the housing 400. Next, as shown in FIG. 11, the upper surface of the element is coated with a protective film such as silicon rubber.

  The operation of the variable inductor type MEMS pressure sensor according to the present invention having the above-described configuration will be briefly described as follows.

ここで、λ：磁歪定数
Ｋ：異方性定数
Ｍ：磁気モーメント
σ：印加された応力
μ_ＡＣ：ＡＣ状態での透磁率 Under AC conditions, the differential equation of permeability with respect to the applied stress of the magnetostrictive material can be expressed as Equations 1 and 2.

Where λ: magnetostriction constant K: anisotropy constant M: magnetic moment σ: applied stress μ _AC : permeability in AC state

  Through equations (1) and (2), it can be seen that if a stress is applied to the magnetostrictive material, the permeability changes, and this change induces a change in inductance. Therefore, the pressure applied to the magnetostrictive material can be calculated by measuring the change in inductance.

ここで、Ｌ：インダクタンス
μ_０：自由空間での透磁率
μ_ｒ：ソレノイドコアの相対透磁率
Ｎ：ソレノイド導線の巻数
Ａ：ソレノイドの断面積
ｌ：ソレノイドの長さ

That is, as shown in FIG. 12, the inductance of the solenoid having the magnetostrictive material as the core is the same as Equation 3, and if compressive stress is applied in the surface (A) direction of the solenoid core, the permeability and stress with respect to the magnetostrictive material The change can be calculated by substituting Equation 1 representing the relationship into Equation 3 below.

Where L: inductance
μ ₀ : Permeability in free space
μ _r : relative permeability of solenoid core
N: Number of turns of solenoid wire
A: Cross section of solenoid
l: Solenoid length

  If pressure is applied to the diaphragm 300 according to such a principle, the diaphragm 300 is warped, and the pressure is transmitted to the dielectric thin film 150 through the pressure introducing groove 180 to deform the dielectric thin film 150.

  FIG. 13 is a diagram illustrating a mode in which pressure is applied to one unit cell in the inductor array unit 100 of FIG. 1. The dielectric thin film 150 is deformed by the pressure, and the dielectric is generated by the stress generated by the deformation. A stress is applied to the magnetostrictive material thin film 120 deposited on the thin film 150. As a result, the magnetostrictive material thin film 120 is deformed, and the relative permeability of the magnetostrictive material thin film 120 is changed by the deformation.

  And if the relative magnetic permeability of the magnetostrictive material thin film 120 which is a solenoid core changes, the inductance of the inductor array part 100 will change like Numerical formula 4.

  When the inductor array unit 100 is a primary inductor and the inductor of an external measuring device (not shown) is a secondary inductor, the energy change of the primary inductor due to the inductance change of the inductor array unit 100 is It is transmitted to the secondary inductor by the inductance action.

  FIG. 14 is a circuit diagram showing the principle of wireless telemetry using mutual inductance. Even if the principle of the circuit as shown in FIG. 14 is applied to the unit cell as shown in FIG. Any of the mathematical formulas used can be used identically.

Ｒ_ｐ：１次側の抵抗（寄生的）
Ｌ_ｐ：１次側のインダクタンス
Ｒ_ｓ：２次側の抵抗（寄生的）
Ｌ_ｓ：２次側のインダクタンス
Ｃ_ｓ：２次側のキャパシタンス（センサー）
Ｍ：相互インダクタンス
Ｋ：カップリング係数
ω_０：共振周波数

ここで、ｋは、二インダクター間のカップリング係数であり、数式７のように表現される。

ここで、ｚ：二つのインダクター間の距離
ｒ_ｐ：２次側インダクター（コイル）の半径
ｒ_ｓ：１次側インダクター（コイル）の半径 That is, the primary-side input impedance at the resonance frequency ω ₀ is as shown in Equation 5, and the mutual inductance M between the primary-side inductor and the secondary-side inductor is as shown in Equation 6.

R _p : primary side resistance (parasitic)
L _p : Inductance on the primary side
R _s : secondary resistance (parasitic)
L _s : Secondary side inductance
C _s : Secondary-side capacitance (sensor)
M: Mutual inductance
K: Coupling coefficient
ω ₀ : resonance frequency

Here, k is a coupling coefficient between two inductors, and is expressed as Equation 7.

Where z is the distance between the two inductors
r _p : Radius of the secondary inductor (coil)
r _s : radius of primary inductor (coil)

  In the external measurement device, the pressure applied to the sensor can be measured wirelessly by calculating the input impedance and calculating the amount of energy change as shown in Equation 5.

Referring to Equations 5 to 7, only when the maximum energy is transmitted from the primary inductor 100 to the secondary inductor, the secondary impedance of Equation 5 is changed greatly. However, such maximum energy is transmitted. The condition is when the resonance frequency f ₀ is generated.

In each unit cell, the pressure introduction groove 180 can be expressed as Equation 8, and the quality factor Q _tank at that time is as Equation 9.

  Therefore, if the pressure introduction groove 180 is enlarged to improve the quality factor, it is advantageous for application of a high frequency or wireless sensor.

Further, Table 1 shows the relationship of the parameters to the size of the pressure introducing portion. As shown in Table 1, the magnetic permeability _{μs of the} sensor is large, and several inductors are connected in series. If the inductor array unit 100 is configured with a structure in which the typical inductance L _S is increased, it is expected that the performance is extremely excellent as compared with the conventional MEMS LC resonance type pressure sensor.

  The variable inductor type MEMS pressure sensor using the magnetostrictive effect according to the present invention has a higher resolution than a conventional piezoresistive or capacitive sensor, and thus has an excellent resolution. In addition, since this variable inductor type MEMS pressure sensor is manufactured using a MEMS processing technology compatible with a semiconductor process, it is possible to achieve miniaturization and high-density mounting, and to reduce production costs. Furthermore, since this pressure sensor can be a non-power / wireless sensor that can measure pressure in a non-powered state without using a power source, it can be used as an implantable or real-time diagnostic system.

It is a top view which shows the structure of the variable inductor type MEMS pressure sensor using the magnetostriction effect by this invention. FIG. 2 is an equivalent circuit diagram of FIG. 1. It is sectional drawing which cut | disconnected the sensor of FIG. 1 in the A-A 'direction. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. FIG. 4 is a cross-sectional view showing a manufacturing process of the inductor array section of FIG. 3. This is a general solenoid model with a magnetostrictive material as a core. 2 is a diagram illustrating a mode in which pressure is applied to one unit cell in the inductor array unit of FIG. 1. It is a circuit diagram which shows the principle of the radio | wireless telemetry using a mutual inductance.

Claims (7)

A plurality of annular electrodes are connected in series on the first substrate to form a coil portion, and a magnetostrictive thin film corresponding to the annular electrode is formed on the second substrate facing the first substrate in parallel at a constant distance. And the coil part and the magnetostrictive material thin film constitute an inductor, and the inductor array part changes the inductance of the inductor by inducing a permeability change of the magnetostrictive material thin film by an external pressure,
A variable inductor type using a magnetostrictive effect, comprising: an inductor array unit and an LC resonance circuit; and a capacitor unit that converts and stores magnetic energy discharged in the inductor array unit into a voltage form. MEMS pressure sensor. The magnetostrictive material thin film is:
2. The variable inductor type MEMS pressure sensor using magnetostriction effect according to claim 1, wherein the MEMS pressure sensor is an amorphous material or a single crystal alloy. The inductor array section is
The first substrate formed on the first surface such that the annular electrodes are connected in series;
The magnetostrictive material thin film is deposited on the second surface opposite to the first surface so as to have a one-to-one correspondence with the annular electrode, and external pressure is applied on the third surface, which is the back surface of the second surface. The second substrate on which pressure introducing grooves to be transmitted to the magnetostrictive material thin film are formed;
3. The spacer according to claim 1, further comprising a spacer that maintains the first substrate and the second substrate at regular intervals so that the annular electrode and the magnetostrictive material thin film are not in direct contact with each other. A variable inductor type MEMS pressure sensor using the magnetostrictive effect. The first substrate is
4. The variable inductor type MEMS pressure sensor using the magnetostriction effect according to claim 3, wherein the variable pressure type MEMS pressure sensor is Pyrex (registered trademark) or quartz glass. The second substrate is
The variable inductor type MEMS pressure sensor using the magnetostriction effect according to claim 3, wherein the MEMS pressure sensor is a dielectric thin film. A diaphragm that protects the top surface of the sensor to which external pressure is applied;
The variable using the magnetostrictive effect according to claim 1, further comprising a housing formed so as to cover an outline of the sensor except for an upper surface of the sensor, and fixing the sensor and the diaphragm. Inductor type MEMS pressure sensor.   A secondary side coil unit that wirelessly transmits a change in inductance of the inductor array unit; and measuring the inductance change of the inductor array unit transmitted through the secondary side coil; The variable inductor type MEMS pressure sensor using the magnetostrictive effect according to claim 1, further comprising a measuring device that measures a pressure applied to the magnetostrictive effect.

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