JP2013040891A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor that, in a diaphragm-type pressure sensor, allows suppression of reduction in sensitivity generated because of a thermal expansion coefficient difference between a vessel and a piezoelectric sensitive element, and moreover has high pressure resistance.SOLUTION: In a diaphragm-type pressure sensor, amorphous silicon carbide layers 11 and 31, and epitaxial SiOlayers 12 and 32 are made to grow on bonding surfaces between each of an upper member 1 and a lower member 3, and a quartz vibrator 2, which are bonded using a surface activation method. Thereby, it can be prevented that stresses are generated on the quartz vibrator 2 because of a thermal expansion coefficient difference caused by making a dissimilar material such as an adhesive sandwiched in the bonding portions, which causes a decrease in detection sensitivity. The use of a silicon material for a vessel enables possession of high pressure resistance.

Description

  The present invention relates to a diaphragm type pressure sensor using a crystal resonator.

  In a TPMS (tire pressure monitoring system) that constantly monitors the tire pressure of a car and issues an alarm when the pressure falls below a set pressure, a pressure sensor using a crystal oscillator is used to measure the pressure. It is being considered.

  The diaphragm type pressure sensor is a sensor that detects a change in resonance frequency caused by a pressure sensitive element supported by the diaphragm, for example, a crystal resonator, when receiving stress from the outside.

  The diaphragm type pressure sensor is a highly sensitive pressure sensor with extremely high sensitivity for detecting the deformation of the diaphragm. However, due to the high sensitivity, even if the diaphragm is slightly deformed due to disturbances other than pressure, deformation may be detected. Examples of the disturbance include a case where stress is generated in the pressure sensitive element due to a difference in thermal expansion coefficient between the container and the pressure sensitive element when the temperature of the environment changes.

  In Patent Document 1, by configuring the container and the pressure sensitive element with a material having a coefficient of thermal expansion, for example, the container and the pressure sensitive element are each composed of silicon and quartz, or both are composed of quartz, A technique for reducing sensitivity reduction due to temperature change is described. However, the pressure-sensitive element is bonded with an adhesive, and the sensitivity is lowered due to a temperature change due to a difference in thermal expansion coefficient between the container and the crystal unit and the bonding material (adhesive). Further, since quartz is used for the container, the pressure sensor has low stress and low pressure resistance.

JP2010-281573

  The present invention has been made under such circumstances, and provides a pressure sensor that can suppress a decrease in sensitivity due to a difference in thermal expansion coefficient between materials of a container and a pressure sensitive element in a diaphragm pressure sensor. There is.

The pressure sensor of the present invention constitutes a diaphragm that bends due to pressure from the outside, an upper member made of silicon with a recess formed on the lower surface side,
A concave member is formed on the upper surface side, and a lower member made of silicon that forms a container together with the upper member;
A quartz crystal in which a peripheral portion of the upper member is sandwiched between the peripheral portion of the upper member and the peripheral portion of the lower member, and a crystal resonator serving as a pressure sensitive element is formed in a space formed by the concave portion. The board,
Silicon dioxide formed in this order from the crystal plate side between the peripheral portion of the crystal plate and the peripheral portion of the upper member and between the peripheral portion of the crystal plate and the peripheral portion of the lower member An epitaxial SiO ₂ layer and a silicon carbide layer comprising:
The upper member, the crystal plate, and the lower member are bonded to each other through the epitaxial SiO ₂ layer and the silicon carbide layer.

The present invention uses a silicon as a material for an upper member and a lower member forming a container of a pressure sensor, and a quartz plate including an upper member and a crystal resonator via an amorphous silicon carbide layer and an epitaxial SiO ₂ layer And the lower member is joined. Since the silicon carbide layer has high elasticity and plays a role as a buffer layer, when the environmental temperature changes, the buffer layer absorbs the difference in thermal expansion coefficient between silicon and quartz, so that the generation of stress is small. , A decrease in detection sensitivity is suppressed. Further, since the silicon carbide layer is firmly surface-bonded to silicon and quartz, the bonding force between the container and the quartz plate is large. Furthermore, the pressure resistance of the pressure sensor is high by using silicon as the container.

It is the vertical side view of the pressure sensor which concerns on embodiment of this invention, and a plane perspective view. It is a top view which shows a part of manufacturing process of the upper member of the said pressure sensor. It is a vertical side view which shows a part of manufacturing process of the said upper member. It is a top view which shows a part of manufacturing process of the lower side member of the said pressure sensor. It is a top view which shows a part of manufacturing process of the said lower side member. It is a top view which shows a part of manufacturing process of the crystal oscillator of the said pressure sensor. It is a vertical side view which shows a part of manufacturing process of the crystal oscillator of the said pressure sensor. It is a perspective view which shows the process of joining the upper side member of the said pressure sensor, a crystal oscillator, and a lower side member. It is the schematic diagram which showed typically a mode that the pressure was added to the pressure sensor which concerns on embodiment of this invention.

  First, the structure of the pressure sensor in the embodiment of the present invention will be described. As shown in FIG. 1, the pressure sensor includes an upper member 1 and a lower member 3 for constituting a container, and a crystal resonator 2 that is a pressure-sensitive element provided between the upper member 1 and the lower member 3. Crystal plate 25 is provided. The upper member 1 and the lower member 3 are each made of silicon. In the upper member 1, a circular recess 13 is formed on the upper surface side of a flat cylindrical shape, and a circular recess 14 having a smaller diameter than the recess 13 is formed on the lower surface side, and the thin wall between these recesses 13, 14 is formed. The portion (bottom portion) is configured as a diaphragm 15. The diameter of the diaphragm 15 is set to about 10 mm, for example. The thickness is 1.4 mm, for example, and it is configured as an elastic plate that bends when pressed.

  The upper surface of the diaphragm 15 faces a measurement atmosphere such as an internal space of a tire provided in the vehicle, and is deformed according to the pressure of the measurement atmosphere. That is, the diaphragm 15 bends to the inside of the container when the pressure of the measurement atmosphere becomes larger than the pressure in the container, and bends to the outside of the container when the pressure becomes small.

  The quartz plate 25 is made of, for example, an AT-cut quartz, and is formed in a strip shape that is cut out by etching as will be described later, and that both ends of the quartz plate 25 are connected to the annular frame 23 and extend in the diameter direction. The crystal piece 24 is formed.

The peripheral edge of the annular frame 23 is sandwiched between the annular wall 16 of the upper member 1 and the annular wall 38 of the lower member 3, and is surrounded by the upper member 1 and the lower member 3. It will be placed in the sealed airtight space. The bonding surfaces of the crystal piece 24 with the upper member 1 and the lower member 3 are epitaxial SiO ₂ layers 12 and 32 made of silicon dioxide having a thickness of 1 to 10 μm and carbonized with a thickness of 50 to 100 μm from the crystal piece 24 side. The silicon carbide layers 11 and 31 of silicon are formed in this order. The crystal resonator 2 is arranged in parallel with the diaphragm 15, that is, opposed to the diaphragm 15, and has a double beam support structure in which both ends are supported.

  Excitation electrodes 21 and 22 are formed on both surfaces of the strip-shaped crystal piece 24 by using, for example, Cr as an underlayer and Au being laminated thereon. The electrodes 21 and 22 are formed from the upper surface side of the annular wall 36 of the lower member 3. It is routed to the outside of the container and connected to the external terminal 36 through a conductive path 39 passing through the through hole 34 penetrating to the lower surface side of the container.

  Next, the manufacturing method of the pressure sensor according to the present invention will be described. First, an upper member wafer 10, a crystal resonator wafer 20, and a lower member wafer 30 are prepared. The upper member and lower member wafers 10 and 30 are made of, for example, silicon. The quartz resonator wafer 20 uses the AT-cut quartz as described above. The outer shapes of the upper member 1, the crystal plate 25, and the lower member 3 are respectively formed on the wafers 10, 20, and 30 by forming a mask by a photolithography process and an etching process.

After the surface of the upper member wafer 10 is subjected to a hydrophilic treatment by RCA cleaning, an amorphous silicon carbide (SiC) layer 11 is formed on one surface as shown in FIG. The silicon carbide layer 11 is a layer provided for growing a heteroepitaxial SiO 2 layer having a large lattice constant difference on silicon, and by providing an amorphous layer having no regular atomic arrangement, for example, a substrate such as silicon is formed. A layer having a different lattice constant such as an epitaxial SiO ₂ layer can be grown thereon. As shown in FIG. 3, silicon carbide layer 11 is formed on the entire surface to be bonded to crystal plate 25. The silicon carbide layer 11 is formed on a silicon substrate at a low temperature of 200 ° C. using a silane (SiH ₄ and oxygen (O ₂ ) as a reaction gas and hydrogen (H ₂ ) as a carrier gas, for example, by a photo-CVD apparatus. A film is formed.

Next, as shown in FIG. 3, an epitaxial SiO ₂ layer 12 is grown on the silicon carbide layer 11 in the upper member wafer 10. The epitaxial SiO ₂ layer 12 is grown at a temperature of silane (SiH ₄ ) and oxygen (O ₂ ) 500 to 570 ° C. as reaction gases using, for example, a photo-CVD apparatus.

After the epitaxial SiO ₂ layer 12 is formed, the upper member 1 is formed with recesses 13 and 14 on the upper surface side and the bonding surface side as shown in FIG. For specific processing, a metal film is formed on both surfaces of the upper member 1 by sputtering, and a metal mask pattern is formed by photolithography. Thereafter, the concave portion 13 is formed on the upper surface portion side of the upper member 1 by, for example, RIE (Reactive Ion Etching) processing, and the concave portion 14 is formed on the bonding portion side by, for example, chemical etching processing. A diaphragm 15 of about 1.4 mm is formed.

On the other hand, the lower member wafer 30 has a bonding surface on the upper surface side. As shown in FIG. 5, a silicon carbide layer 31 is grown on the bonding surface at a low temperature as shown in FIG. 5 after RCA cleaning as in the case of the upper member 1, and then on the silicon carbide layer 31 as shown in FIG. An epitaxial SiO ₂ layer 32 is formed so as to cover the entire surface.

  Next, as shown in FIG. 5, the lower member 3 is provided with a recess 33, and the through hole 34 through which the wiring 35 passes is vertically penetrated from the upper surface portion of the annular wall 38 of the lower member 3 to the lower surface portion side. The conductive path 39 for connecting the electrodes 21 and 22 provided in the crystal resonator 2 is formed. The through hole 34 is formed by, for example, sand blasting.

  Next, a wiring 35 is formed in the through hole 34, and an external terminal portion 36 is formed on the lower surface portion of the lower member 3. The wiring 35 provided in the through hole 34 is formed by, for example, filling the through hole 34 with a conductive material such as paste-like Au, and is joined to the external terminal portion 36. On the upper surface portion side of the lower member 3 of the wiring, a joint portion 37 for connecting to electrodes 21 and 22 provided on the crystal resonator 2 described later is provided.

  Electrodes 21 and 22 are formed on both sides of the crystal piece 24 as shown in FIGS. The electrode 21 is routed from the central part on the upper surface side of the crystal piece 24 corresponding to the excitation electrode to the lower surface side of the annular member 23 via one end side, and corresponds to one connecting portion 37 provided on the lower member 3. Stretched to position. The electrode 22 is drawn from the position corresponding to the other connecting portion 37 to the central portion along the lower surface portion of the crystal piece 24 and is formed so as to sandwich the crystal piece 24 between the electrodes 21 and 22 formed on both surfaces.

Subsequently, as shown in FIG. 8, the upper member 1, the crystal plate 25, and the lower member 3 are overlapped and joined to each other in this order in a state in which the respective positions in the plane direction are aligned. As a result, the crystal plate 25 is joined so as to be sandwiched from above and below by the epitaxial SiO ₂ layers 12 and 32 provided on the upper member 1 and the lower member 3, respectively. The upper member 1 and the crystal plate 25 are bonded at room temperature by surface activation bonding using, for example, an argon beam. On the other hand, the lower member 3 and the crystal plate 25 are bonded at room temperature by surface activation bonding using oxygen plasma, and the electrodes 21 and 22 and the wiring bonding portion 37 are electrically connected. Thereafter, dicing is performed to separate the pressure sensors.

  Next, the operation of the pressure sensor according to the above embodiment will be described. The upper member 1 of the pressure sensor of the present invention is attached to, for example, a tire valve. At this time, the inside of the tire is in a pressurized state (atmosphere above atmospheric pressure), and the disk portion of the diaphragm 15 bends inward of the container according to the pressure. The annular wall 16 of the upper member is pushed outward in accordance with the amount of bending, so that the crystal resonator 2 in the length direction of the crystal resonator 2 joined through the annular wall 16 of the upper member 1 is expanded. A tensile stress is applied, and the crystal resonator 2 is bent as shown in FIG. Due to this bending, the resonance frequency of the crystal unit 2 is changed, and the frequency signal is measured by the measurement circuit unit via the external terminal 36 and the external conductive path and the oscillation circuit (not shown), thereby detecting the pressure value. .

According to the above-described embodiment, silicon is used for the upper member 1 and the lower member 3 forming the container of the pressure sensor, and the amorphous silicon carbide layers 11 and 31 and the epitaxial SiO ₂ layers 12 and 32 are formed. The upper member 1, the crystal plate 25 including the crystal resonator 2, and the lower member 3 are joined to each other. Since the silicon carbide layers 11 and 31 have a large elasticity and play a role of a buffer layer, when the environmental temperature changes, the difference in thermal expansion coefficient between the silicon containers 1 and 3 and the crystal piece 24 is determined. Since the layers 11 and 31 absorb, the generation of stress is small, and the decrease in detection sensitivity is suppressed.

  Further, since the silicon carbide layers 11 and 31 are amorphous and do not have a specific atomic arrangement, the arrangement of atoms on the bonding surface can be matched, and the container and the quartz crystal are firmly bonded to silicon and the quartz crystal. The bonding force with the plate 25 is large.

  In addition, a pressure sensor with high strength can be obtained by using silicon as a container and holding a crystal between silicon substrates.

1 Upper member 11, 31 Silicon carbide layer 12, 32 Epitaxial SiO ₂ layer 15 Diaphragm 2 Crystal resonator 21, 22 Electrode 3 Lower member 35 Wiring 36 External terminal

Claims (1)

An upper member made of silicon that forms a diaphragm that bends due to pressure from the outside and that has a recess formed on the lower surface side;
A concave member is formed on the upper surface side, and a lower member made of silicon that forms a container together with the upper member;
A quartz crystal in which a peripheral portion of the upper member is sandwiched between the peripheral portion of the upper member and the peripheral portion of the lower member, and a crystal resonator serving as a pressure sensitive element is formed in a space formed by the concave portion. The board,
Silicon dioxide formed in this order from the crystal plate side between the peripheral portion of the crystal plate and the peripheral portion of the upper member and between the peripheral portion of the crystal plate and the peripheral portion of the lower member An epitaxial SiO ₂ layer and an amorphous silicon carbide layer comprising:
The pressure sensor, wherein the upper member, the crystal plate, and the lower member are bonded to each other through the epitaxial SiO ₂ layer and the silicon carbide layer.

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