CN113758613B - SOI-based resistance center placed piezoresistive pressure sensor - Google Patents

Abstract

The invention provides a piezoresistive pressure sensor with resistor center placed based on SOI, which improves effective stress in piezoresistors by placing two piezoresistors in the center of a film, thereby improving the output sensitivity of the sensor and reducing the output nonlinearity. In addition, silicon is used as a lead structure, the resistance value of the lead is the lowest through special design and is symmetrical in the bridge, and the manufacturing process is greatly simplified. The invention mainly relates to the field of design and micro-processing of piezoresistive pressure sensors.

Description

SOI-based resistive center-placed piezoresistive pressure sensor

Technical Field

The invention relates to the technical field of MEMS (micro-electromechanical systems) microsensors, in particular to a piezoresistive pressure sensor with a resistor placed in the center based on an SOI (silicon on insulator).

Background

The piezoresistive pressure sensor takes a piezoresistor element as a core component, has the advantages of low cost, low power consumption, high precision, easiness in batch manufacturing and the like, and is widely applied to the fields of medical diagnosis, industrial control, vehicle engineering, aerospace, meteorological monitoring and the like.

Pressure sensors can be classified into capacitance type, resonance type, piezoelectric type, piezoresistive type, and the like according to the detection principle. The pressure sensitive elements of the capacitive pressure sensor are a group of capacitors, the pressure to be detected is detected by detecting the change of the capacitors, and the capacitive pressure sensor has the advantages of low power consumption, high sensitivity, high response speed and the like, but the capacitive piezoresistive sensor has weak output signals, high nonlinearity and low signal-to-noise ratio, so the application of the capacitive pressure sensor is limited; the resonant pressure sensor accurately reflects the pressure to be measured by utilizing the change of the resonant frequency of the resonant beam, and has the advantages of high precision, high resolution, good stability and the like, but the resonant pressure sensor is easily influenced by the vacuum degree, the manufacturing process is relatively complex, and the yield is low; the piezoelectric pressure sensor directly converts pressure to be measured into a voltage or charge signal through the piezoelectric crystal, has high working frequency, good stability and quick dynamic response, but has poor capability of measuring a low-frequency pressure signal, is easy to be influenced by the environment, and can only be applied to a few fields. The piezoresistive pressure sensor has the advantages of small volume, high precision and simple manufacturing process, and is one of the most widely applied pressure sensors.

The piezoresistive pressure sensor takes a piezoresistor as a pressure sensitive element. Under the external pressure, the pressure sensitive film and the piezoresistor on the pressure sensitive film deform, so that the resistance value of the piezoresistor changes. By means of the wheatstone bridge, a change in the resistance value can be translated into a corresponding voltage output. The sensitivity and linearity of the output voltage are two key parameters for measuring the performance of piezoresistive sensors, high sensitivity generally means high resolution and high signal-to-noise ratio, and high linearity enables the output variation of the sensor to be better predicted, thereby simplifying the circuit and increasing the accuracy of the sensor.

Generally, the simplest way to increase the sensitivity is to reduce the thickness of the pressure sensitive membrane so that the membrane deforms more under a certain pressure and thus more stress in the area of the piezoresistor. However, this method also increases the nonlinearity of the deformation of the film, so that the output performance of the sensor is deteriorated. In addition, a frequently used method is to use a beam-film composite structure, namely a beam-type stress concentration structure is manufactured on the front surface of the film, and the stress near the piezoresistor is increased on the premise of not increasing the non-linearity of the deformation of the film, so that the sensitivity of the sensor is increased. However, this method requires additional etching on the front surface of the thin film, which makes the manufacturing process of the sensor more complicated.

In addition, in addition to the non-linearity of the deformation of the membrane, stress matching between the piezoresistors is also one of the key factors affecting the linearity of the output of the sensor. It is generally required that under a certain applied pressure, the four piezoelectric groups have stresses with equal absolute values and opposite magnitudes. The greater the difference in absolute values of stress between the piezoresistors, the higher the non-linearity of the output of the wheatstone bridge. Therefore, the stress matching problem between the piezoresistors must be considered also in the structural design.

Metallic materials are commonly used for electrical connection between piezoresistors to form a complete wheatstone bridge, however, the use of metallic materials presents some problems: 1. additional photoetching, evaporation/sputtering processes are required, so that the manufacturing period and cost of the sensor are increased; 2. the thermal expansion coefficient difference between the metal material and the piezoresistor is large, and when the metal material is directly connected with the piezoresistor, large thermal stress can be generated, and the thermal performance of the sensor is influenced.

Disclosure of Invention

In view of the above, the present invention is directed to an SOI-based resistive-center-placed piezoresistive pressure sensor, which is intended to solve the above technical problems.

To achieve the above object, the present invention provides an SOI-based resistive-center placed piezoresistive pressure sensor, comprising:

the sensor comprises a sensor core body and a glass plate, wherein the sensor core body and the glass plate are bonded together through an anode; wherein, the first and the second end of the pipe are connected with each other,

the sensor core body comprises a device layer, an oxygen burying layer and a substrate layer, wherein the oxygen burying layer is clamped between the substrate layer and the device layer;

a pressure sensitive film is manufactured on the substrate layer;

a plurality of piezoresistors, silicon leads and lead electrodes are manufactured on the device layer;

the four piezoresistors are arranged on the central line of the pressure sensitive film along the longitudinal direction, two piezoresistors in the four piezoresistors are arranged at the edge position of the pressure sensitive film, and the other two piezoresistors in the four piezoresistors are arranged at the central position of the pressure sensitive film. The piezoresistors face the [110] direction of the Si crystal.

The piezoresistors are connected through silicon wires, and lead electrodes are connected to the silicon wires connecting the two adjacent piezoresistors. Further, electric signal isolation grooves are formed between different silicon wires and between the silicon wires and the piezoresistors.

Furthermore, the electrical signal isolation grooves formed by etching form electrical isolation among different silicon wires and between the silicon wires and the piezoresistors, so that a complete Wheatstone bridge structure is formed.

Further, the buried oxide layer forms an electrical isolation between the device layer and the substrate layer.

Further, the four piezoresistors are connected through a silicon wire to form a Wheatstone bridge structure. The piezoresistor is a square structure protruding out of the pressure sensitive film, and the bottom of the piezoresistor is directly connected with the buried oxide layer. The lateral cross-section of the varistor is square protruding from the surface of the buried oxide layer.

Further, the silicon wire is an electrical connection structure.

Further, the placing of two of the four piezoresistors at the edge position of the pressure-sensitive membrane comprises: on the pressure sensitive film, the maximum value of the longitudinal stress is in the center of two opposite edges of the pressure sensitive film and is a positive value; the two piezoresistors are respectively placed at the centers of the two opposite edges.

Further, the placement of the other two piezoresistors of the four piezoresistors at the center position of the pressure-sensitive membrane comprises: on the pressure sensitive film, the minimum value of the longitudinal stress is in the center of the pressure sensitive film, the longitudinal stress is negative, and the other two piezoresistors are placed in the center of the pressure sensitive film.

Further, the piezoresistors have identical structures.

Furthermore, the piezoresistor is formed by etching, and the thickness of the piezoresistor is equal to the thickness of the device layer.

Furthermore, the electric signal isolation groove is formed by etching, and the thickness of the electric signal isolation groove is equal to the thickness of the device layer. The remaining silicon material of the pressure sensitive film area is used as a silicon wire, except for the electrical signal isolation groove and the piezoresistor.

Further, the glass plate comprises a glass plate material and a getter, the getter is manufactured on the glass plate material, the glass plate is bonded with the bottom of the SOI substrate layer, a vacuum reference cavity is formed, and the getter is located in the vacuum reference cavity. The vacuum reference chamber has no remaining components.

Further, a getter is deposited at the bottom of the groove.

Further, a metal thin film electrode is evaporated on the lead electrode.

Further, the getter comprises a Ti-based getter.

Further, the metal thin film electrode on the lead electrode comprises one or more of Cr/Au, al or Cu.

Furthermore, the piezoresistor, the silicon wire structure and the lead electrode are all made of p-type silicon and simultaneously play roles in pressure sensitivity and electric connection.

Further, the remaining silicon material of the thin film region is used as an electrical connection structure to reduce the resistance of the conductive line as much as possible, except for the necessary electrical signal isolation groove and the piezo-resistor. In terms of shape, the silicon wire structure is a generally square structure, the aspect ratio is basically the same, and the sheet resistance basically reaches the minimum value of 1.

The piezoresistors are manufactured by utilizing the device layer of the SOI, the thickness of the piezoresistors is consistent with that of the device layer, the four piezoresistors are all arranged on the central line of the pressure sensitive film along the longitudinal direction, two piezoresistors are arranged at the edge position of the film, the resistance change of the piezoresistors is positively correlated with the pressure, the other two piezoresistors are arranged at the central position of the film, and the resistance change of the resistors is negatively correlated with the pressure. Since the piezoresistor of the SOI structure has a certain thickness, the stress of the pressure-sensitive film will be gradually lost in the process of transferring to the upper part of the piezoresistor along the thickness direction. Meanwhile, since the aspect ratio of the varistor is generally large, the transverse stress loss in the width direction thereof is severe and the longitudinal stress loss in the length direction thereof is small. Thus, it can be approximated that the piezoresistor is stressed only longitudinally and not transversely. On the pressure sensitive membrane, the longitudinal stress at the edge of the membrane is the maximum positive value, and the longitudinal stress at the center of the membrane is the minimum negative value. Therefore, placing two piezoresistors at the edge of the film and two piezoresistors at the center of the film will maximize the output of the Wheatstone bridge, thereby maximizing the sensitivity of the sensor without using an additional stress concentration structure. Meanwhile, the absolute value difference of the longitudinal stress of the piezoresistor at the edge of the film and the piezoresistor at the center of the film is not large, and the balance of the Wheatstone bridge is not obviously influenced, so that the high linearity of the output of the Wheatstone bridge is ensured.

A small area of the sensor core device layer is etched to form electrical insulation, and a large area is reserved to form a conducting wire structure between the piezoresistors. The method does not need to carry out additional metal wire deposition, thereby greatly simplifying the process. And moreover, the direct contact between the metal and the piezoresistor structure is also avoided, the thermal stress caused by thermal mismatch is eliminated, and the thermal performance of the sensor is improved. The area of the silicon wire structure is large enough and is designed into a square shape, so that the sheet resistance of the silicon wire structure is minimized, and the resistance value of the silicon wire is minimized. In addition, the four silicon wires are basically symmetrical in shape, so that the balance of the Wheatstone bridge is not basically influenced while electric signals are conducted, and the performance of the sensor is not basically influenced.

As another aspect of the present invention, there is provided a method of manufacturing a piezoresistive pressure sensor, including the steps of:

a, etching a vacuum cavity on an SOI substrate layer;

b, forming a piezoresistor, a lead structure and a lead electrode on the SOI device layer by one-step etching, and etching to the buried oxide layer to stop automatically;

step C: evaporating getter material on the glass plate material to make the vacuum reference cavity reach high vacuum degree;

step D: bonding the glass plate and the SOI by anodic bonding to manufacture a vacuum reference cavity;

step E: evaporating an aluminum electrode on the SOI device layer so as to lead out an electrical signal of the Wheatstone bridge;

based on the technical scheme, the piezoresistive pressure sensor disclosed by the invention at least has one of the following beneficial effects:

1. the two piezoresistors are arranged in the center of the film, so that the longitudinal stress borne by the piezoresistors is improved, the resistance variation of the piezoresistors under given pressure is increased, and the sensitivity of the sensor is improved; in addition, the two piezoresistors are placed in the center of the film, so that the difference of the stress absolute values of the four piezoresistors is reduced, and the linearity of the sensor is improved;

2. the silicon of the SOI device layer is used for manufacturing the lead for connecting the piezoresistor, so that the steps of metal film deposition, metal film stripping and the like are omitted, the process is simplified, the direct connection between metal and the piezoresistor is avoided, and the influence of stress caused by thermal mismatch on the piezoresistor is avoided. In addition, the area of the silicon wire is designed to be as large as possible and to have a substantially identical and symmetrical square pattern design so that the balance of the wheatstone bridge and the linearity of the bridge output voltage are not substantially affected.

Drawings

FIG. 1 is a three-dimensional perspective view of a resistive-center-placed piezoresistive pressure sensor in accordance with an embodiment of the present invention;

FIG. 2 is a schematic diagram of a thin film region structure of a device layer in a sensor core according to an embodiment of the present invention;

FIG. 3 is a schematic view of a varistor lamination according to an embodiment of the invention;

FIG. 4 is a schematic diagram of a Wheatstone bridge in a sensor core according to an embodiment of the invention;

FIG. 5 is a schematic view of a backside vacuum chamber and a glass plate according to an embodiment of the invention;

wherein in the above drawings, the specific meanings of the attached drawing designations are as follows:

100-SOI device layer;

200-SOI buried oxide layer;

300-an SOI substrate layer;

310-vacuum reference chamber;

101. 102, 103, 104-four piezoresistors;

102a, 102b, 102c, 102d, 102e — layers of different thicknesses of the piezo-resistor 102;

102e, 102f, 102g, 102h, 102i — low stress regions in different thickness layers of the piezo-resistor 102;

111. 112, 113, 114-four lead electrodes of a wheatstone bridge;

121. 122, 123, 124-silicon wire structure connected with piezoresistors;

130-electrical signal isolation slot;

140-device layer frame;

150-pressure sensitive membrane;

160-wheatstone bridge;

400-a glass sheet material;

410-getter material.

Detailed Description

It should be noted that the directional terms, such as "upper", "lower", "left", "right", etc., mentioned in the present embodiment are only used as reference for the direction of the drawings, and are not used to limit the protection scope of the present invention;

in order to make the objects, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings in combination with the specific embodiments;

as one aspect of the invention, an SOI-based resistive-center placed piezoresistive pressure sensor is provided. Referring to fig. 1, a three-dimensional perspective view of a piezoresistive pressure sensor according to an embodiment of the present invention is shown, in which the piezoresistive pressure sensor mainly comprises two parts, namely a sensor core (including an SOI device layer 100, an SOI buried oxide layer 200, and an SOI substrate layer 300) and a glass plate (including a glass plate material 400 and a getter material 410). The buried oxide layer 200 is sandwiched between the substrate layer 300 and the device layer 100. The substrate layer 300 is fabricated with a pressure sensitive membrane 150. The device layer 100 has a device layer bezel 140. In the area of the pressure-sensitive film 150, four piezoresistors 101, 102, 103, 104, silicon conductor structures 121, 122, 123, 124 connecting the piezoresistors, and four lead electrodes 111, 112, 113, 114 of a wheatstone bridge 160 are fabricated on the device layer 100. The four piezoresistors 101, 102, 103, 104 are all arranged on the central line of the pressure sensitive film along the longitudinal direction. Two piezoresistors 101 and 104 are respectively arranged at the left edge and the right edge of the pressure sensitive film 150, and the other two piezoresistors 102 and 103 are arranged at the center of the pressure sensitive film. The piezoresistors are connected through a silicon wire structure to form a Wheatstone bridge structure. And lead electrodes are connected to the silicon wire structures connecting two adjacent piezoresistors. There are electrical signal isolation slots 130 between different silicon wire structures, between the silicon wire structures and the piezoresistors.

Referring to fig. 2, which is a schematic structural diagram of the device layer thin film region 150 in the sensor core according to the embodiment of the present invention, etching is performed to penetrate through the entire device layer 100, and the etching is not stopped until the buried oxide layer 200. The etched electrical signal isolation trenches 130 provide electrical isolation between the different silicon conductors and between the conductors and the piezoresistors, forming a complete wheatstone bridge 160 structure. At the same time, the buried oxide layer 200 forms an electrical isolation between the device layer 100 and the substrate layer 300. Different from PN junction, the silicon dioxide has good stability and can realize stable electrical isolation at high temperature, thereby avoiding the generation of leakage current, fundamentally improving the temperature stability of the sensor and enabling the device to work at high temperature.

The basic principle of the piezoresistors is to produce a change in resistance under stress that is proportional to the magnitude of the stress, thereby enabling the wheatstone bridge 160 to produce a greater voltage output. In the embodiment of the invention, the four piezoresistors 101, 102, 103 and 104 face to the [110] direction of the Si crystal, and in the direction, the resistance variation of the piezoresistors is in direct proportion to the longitudinal and transverse stress difference of the resistors. That is, the larger the longitudinal (lengthwise) stress the resistor is subjected to, the smaller the transverse (widthwise) stress, and the larger the resistance change amount of the varistor.

In the embodiment of the present invention, the SOI device layer 100 is used to fabricate the piezoresistor, the thickness of the device layer 100 is the thickness of the piezoresistor, and the thickness of the device layer 100 in the embodiment of the present invention is 2 μm. Since the piezoresistor can be regarded as a square structure protruding out of the film, the internal stress is different from the stress on the film. The thicker the thickness of the varistor, the greater this stress difference. Therefore, it is not possible to place four piezoresistors in the areas of maximum film stress, i.e., in the center of the four edges of the film, with reference to the stress distribution on the film alone. Since the varistor has a certain thickness, even if it is placed in a region of the film where the stress is the greatest, the average stress inside the varistor may not be able to reach the maximum.

Fig. 3 shows a longitudinal and transverse cross-sectional view of a varistor 102 in accordance with an embodiment of the present invention. To facilitate the explanation of stress and strain in layers of different thicknesses, a single varistor is divided into several layers of a certain thickness. For the sake of convenience of description, the piezoresistors are divided into 5 thickness layers 102a, 102b, 102c, 102d, 102 e. The layer 102a is located at the bottom of the varistor 102 and is directly connected to the buried oxide layer 200, and the layer 102e is located at the top of the varistor 102.

The length of the varistor is much longer than the thickness as seen in the longitudinal direction of the varistor, so the longitudinal cross-section of the varistor 102 can be seen as a rectangle with a large aspect ratio protruding from the surface of the buried oxide layer 200. When the membrane is bent downwards, the lowermost region 102a of the varistor, because it is directly connected to the membrane, will generate substantially the same compressive strain and substantially the same longitudinal stress as the membrane region. Under small deformations, silicon has the properties of an elastic material, and strain and stress will be lost when transmitted upwards. Thus, the region 102b directly connected to the region 102a will produce a slightly smaller strain than the region 102 a. Meanwhile, since the two ends of the region 102b are floating, a small low stress region 102g will be formed at the two ends. The stress of region 102g is close to 0 so that the absolute value of the mean longitudinal stress of region 102b is slightly reduced. During the upward transfer, the strain and stress continue to decrease, and the area of the gray low stress region continues to increase. In the top region 102e of the varistor 102, the compressive strain caused by film deformation is minimal and the area of the low stress region 102j is maximal, so that the absolute value of the mean longitudinal stress of the region 102e is also minimal.

The low stress regions with different occupation areas at different thicknesses are connected with each other, and two inverted triangular low stress regions are formed on the longitudinal section of the piezoresistor 102. The stress in this region is small and can be considered substantially 0, and is present at two corners of the upper surface of the varistor 102. The stress in the inner regions of the varistor 102, other than these two regions, is substantially unaffected, as is the stress on the membrane. Since the length of the varistor 102 is long and the low-stress region occupies only a small area, the absolute value of the average longitudinal stress of the varistor 102 is only slightly reduced.

The width and thickness of the varistor are not much different from each other in the transverse direction of the varistor, so the transverse cross section of the varistor 102 can be regarded as a square protruding from the surface of the buried oxide layer 200. Similar to the analysis of longitudinal stress, two low stress regions still exist in the transverse cross section of the varistor 102. However, since the width of the varistor 102 is narrow and is equal to or shorter than the length of the low stress region, the low stress regions are overlapped together and occupy most of the transverse cross-section of the varistor 102, so that the absolute value of the average transverse stress of the varistor 102 is greatly reduced to be close to 0.

The piezoresistors 101, 103 and 104 have the same structure as the piezoresistor 102, so that the stress distribution regularity is the same. From the above analysis, it is known that since the piezoresistors 101, 102, 103, and 104 have a certain thickness, the longitudinal stress is reduced slightly and the transverse stress is reduced greatly with respect to the film stress. Therefore, it can be approximated that the piezoresistors 101, 102, 103, 104 are stressed only in the longitudinal direction and not in the transverse direction.

In the design of the embodiment of the invention, the change of the resistance value of the piezoresistor is in direct proportion to the difference of the longitudinal stress and the transverse stress of the piezoresistor. From the above analysis approximation, it can be considered that the variation of the resistances of the piezoresistors 101, 102, 103 and 104 in the embodiment of the present invention is only proportional to the longitudinal stress of the piezoresistors.

On film 150, the maximum value of the longitudinal stress is positive at the center of the left and right edges, and the minimum value of the longitudinal stress is negative at the center of the film. Therefore, two piezoresistors 101 and 104 are arranged at the left edge and the right edge of the film, and the other two piezoresistors 102 and 103 are arranged at the center of the film, so that each piezoresistor can obtain the maximum resistance value variation, the output voltage of the Wheatstone bridge is increased, and the sensitivity of the sensor output is improved.

In the film 150, the longitudinal stress at the left and right edges is the maximum positive value, the longitudinal stress at the upper and lower edges is a negative value having a small absolute value, and the longitudinal stress at the center of the film is a negative value having a large absolute value. If the piezoresistors 101 and 104 are placed at the centers of the left and right edges and the piezoresistors 102 and 103 are placed at the centers of the upper and lower edges, the stress of the piezoresistors 101 and 104 is much larger than the absolute value of the stress of the piezoresistors 102 and 103, and the resistance variation among the four piezoresistors has large mismatch, so that the linearity of the output of the wheatstone bridge 160 is poor; in the embodiment of the invention, the piezoresistors 102 and 103 are arranged in the center of the film, the absolute value of the longitudinal stress at the position is closer to the left edge and the right edge, the mismatch of the resistance variation among the four piezoresistors is reduced, and the linearity of the output of the Wheatstone bridge 160 is improved.

By etching the SOI device layer 100, the piezoresistors 101, 102, 103, 104, the silicon wire structures 121, 122, 123, 124 and the lead electrodes 111, 112, 113, 114 are fabricated in one step without extra steps. All the above structures are p-type silicon and simultaneously assume pressure sensitivity and electrical connection functions.

The silicon connection structures 121, 122, 123, 124 are as large in area as possible. In fact, the remaining silicon material of the thin film region is used as an electrical connection structure to reduce the resistance of the conductive lines as much as possible, except for the necessary electrical signal isolation trenches 130 and the piezoresistors 101, 102, 103, 104. The silicon wire structures 121, 122, 123, 124 are substantially square structures in shape, have substantially the same aspect ratio, and have a sheet resistance of substantially a minimum value of 1, thereby minimizing the resistivity of the wire in shape so that the wheatstone bridge is still dominated by the piezoresistors.

Because a silicon wire structure with certain resistance is used, the wire part will be divided into a part of the input voltage of the wheatstone bridge 160, so that the effective voltage applied to the piezoresistors 101, 102, 103 and 104 is slightly reduced, and the output voltage of the wheatstone bridge will be slightly reduced; in addition, because the silicon wire structure is located at four symmetrical positions, the balance of the bridge cannot be damaged, the wheatstone bridge 160 is still dominated by the piezoresistors, and the linearity of the output of the bridge cannot be influenced;

all piezoresistors, silicon leads and lead electrodes are made of silicon of the device layer, and all parts are integrated, so that the structure of the front device layer can be finished only by one etching step without redundant metal film deposition steps, and the process steps are greatly simplified. In addition, because no metal is in direct contact with the piezoresistor, thermal mismatch caused by the metal and the piezoresistor cannot exist, and the thermal performance of the device can be improved.

Fig. 4 is a schematic diagram of a wheatstone bridge in a sensor core according to an embodiment of the present invention. The four piezoresistors 101, 102, 103 and 104 are connected in series through silicon wire structures 121, 122, 123 and 124 respectively to form a wheatstone bridge 160. Four lead electrodes 111, 112, 113, and 114 are connected to the four silicon wire structures 121, 122, 123, and 124, respectively. And a metal electrode is evaporated on the lead electrode.

FIG. 5 is a schematic view of a backside vacuum chamber and a glass plate according to an embodiment of the invention. The glass plate 400 includes a glass plate material on which the getter is fabricated and a getter. The glass plate 400 is bonded to the bottom of the SOI substrate layer 300 to form the vacuum reference cavity 310 such that the getter is located within the vacuum reference cavity 310. There are no remaining components within the vacuum reference chamber 310.

So far, the structural features of the piezoresistive pressure sensor in this embodiment have been described.

As another aspect of the present invention, a method for manufacturing a piezoresistive pressure sensor is provided, which comprises the following specific steps:

step A: and etching the pressure sensitive film on the back surface of the SOI substrate layer by using the photoresist as a mask and utilizing a deep reactive ion etching technology. Because the depth to be etched is deeper, more viscous photoresist is needed to be used for photoetching so as to achieve thicker thickness, and the ion etching with enough cycles can be resisted;

and B: and etching the piezoresistor, the silicon wire and the lead electrode on the front surface of the SOI device layer by using the photoresist as a mask and utilizing a deep reactive ion etching technology. Because the depth of the etching is shallow and the pattern needs high precision, thinner photoresist is needed for photoetching so as to achieve the pattern with thinner thickness and higher precision;

and C: manufacturing a glass plate with a getter, mainly comprising the following substeps;

substep C1: laser machining is used to ablate patterned vias in the other glass plate corresponding to the locations where getters are to be deposited. Then cleaning the glass sheet to manufacture a hard mask;

and a substep C2: cleaning a glass plate material for anodic bonding, and performing surface activation;

substep C3: sticking the hard mask and the glass plate material together by using a high-temperature adhesive tape, and evaporating the getter;

step D: bonding the glass plate with the getter and the bottom surface of the SOI substrate layer by anodic bonding to form a vacuum reference cavity 310, so that the getter material is positioned in the vacuum reference cavity, and no other part is arranged in the vacuum reference cavity;

step E: making a hard mask of an aluminum electrode, and then evaporating a metal electrode on a lead electrode of a device layer of the SOI by using the hard mask:

so far, the preparation process of the piezoresistive pressure sensor shown in fig. 1 is completed;

up to this point, the present embodiment has been described in detail with reference to the accompanying drawings. It is noted that in the drawings or in the description text, undescribed implementations are all in a form known to those of ordinary skill in the art and are not described in detail. In addition, the above definitions of the respective elements and methods are not limited to the various specific structures, shapes, manners, and the like mentioned in the embodiments, and those skilled in the art may make simple modifications or substitutions.

(1) Getters made at the bottom of the glass grooves include, but are not limited to, ti-based getters or other commercially available getters;

(2) The metal thin-film electrodes on the device layer lead electrodes include, but are not limited to, cr/Au, al, cu, etc.

In summary, the invention provides a piezoresistive pressure sensor with resistor center placed based on SOI, and two piezoresistors are placed in the center of a film, and the other two piezoresistors are placed at the edge of the film, so that the output sensitivity of the sensor is improved, and the output nonlinearity of the sensor is reduced; in addition, silicon rather than aluminum is used as the lead structure, so that the manufacturing process of the sensor is greatly simplified on the premise of not influencing the performance of the sensor, the thermal performance of the sensor is improved, and the lead structure plays a very positive role in improving the comprehensive performance index of the sensor.

The above-mentioned embodiments, which are intended to illustrate the objects, aspects and advantages of the present invention, should be understood as being merely exemplary embodiments of the present invention, not limiting the present invention, and all modifications, equivalents and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (7)

1. The piezoresistive pressure sensor based on SOI and with the resistance center placed is characterized by comprising a sensor core body and a glass plate, wherein the sensor core body and the glass plate are bonded together through an anode; wherein the content of the first and second substances,

the sensor core body comprises a device layer, an oxygen burying layer and a substrate layer, wherein the oxygen burying layer is sandwiched between the substrate layer and the device layer;

four piezoresistors, silicon leads and lead electrodes are manufactured on the device layer;

a pressure sensitive film is manufactured on the substrate layer;

the four piezoresistors are longitudinally arranged on the central line of the pressure sensitive film, two piezoresistors in the four piezoresistors are arranged at the edge position of the pressure sensitive film, and the other two piezoresistors in the four piezoresistors are arranged at the central position of the pressure sensitive film; the piezoresistor faces to the [ 10] direction of the Si crystal;

the piezoresistors are connected through silicon wires, and lead electrodes are connected to the silicon wires connecting the two adjacent piezoresistors; the step of placing two piezoresistors in the edge position of the pressure sensitive film comprises the following steps: on the pressure sensitive film, the maximum value of the longitudinal stress is in the center of two opposite edges of the pressure sensitive film and is a positive value; placing the two piezoresistors at the centers of the two opposite edges respectively; the other two piezoresistors in the four piezoresistors are placed in the central position of the pressure sensitive film, and the method comprises the following steps: on the pressure sensitive film, the minimum value of the longitudinal stress is in the center of the pressure sensitive film, the longitudinal stress is a negative value, and the other two piezoresistors are placed in the center of the pressure sensitive film; the four piezoresistors have the same structure.

2. The sensor of claim 1, wherein the piezoresistors, the silicon leads and the lead electrodes are all p-type silicon, and perform both pressure-sensitive and electrical connection functions.

3. The sensor of claim 1, wherein the piezoresistors are formed by etching to a thickness equal to the device layer thickness.

4. The sensor according to claim 1, wherein there are electrical signal isolation grooves between different silicon wires, between the silicon wires and the piezoresistors, the electrical signal isolation grooves are formed by etching and have a thickness equal to the thickness of the device layer; the remaining silicon material of the pressure sensitive film area is used as a silicon wire, except for the electrical signal isolation groove and the piezoresistor.

5. The sensor of claim 1, wherein the glass plate comprises a glass plate material and a getter, the getter is fabricated on the glass plate material, and the glass plate is bonded to the bottom of the substrate layer to form the vacuum reference cavity such that the getter is located in the vacuum reference cavity.

6. The sensor of claim 1, wherein the lead electrodes have evaporated metal thin film electrodes thereon comprising one or more of Cr/Au, al, or Cu.

7. Method for manufacturing a piezoresistive pressure sensor according to any of the claims 1-6, comprising the steps of:

step A: etching a vacuum cavity on the SOI substrate layer;

and B, step B: forming a piezoresistor, a lead structure and a lead electrode on the SOI device layer by one-step etching, and etching to the buried oxide layer to be self-stopped;

and C: evaporating getter material on the glass plate material to make the vacuum reference cavity reach high vacuum degree;

step D: bonding the glass plate and the SOI by anodic bonding to manufacture a vacuum reference cavity;

step E: and evaporating an aluminum electrode on the SOI device layer so as to facilitate the derivation of the electric signal of the Wheatstone bridge.

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