Patent Application
20190204171
The present disclosure relates to a pressure sensor.
A pressure sensor having a structure, in which a sensor chip forming a diaphragm is joined to a base and the base is attached to a pedestal provided by a package via an adhesive, is known.
A pressure sensor may include a sensor chip and a support member. The sensor chip may include a diaphragm and an inner space. The support member may support the sensor chip at a position separated from the diaphragm. An outer shape of the sensor chip may be provided by a polygonal shape or a circular shape. An outer shape of the diaphragm may be provided by a polygonal shape or a circular shape.
The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
For example, in a type of pressure sensors, offset fluctuation in the sensor output occurs due to internal stress such as mounting stress and thermal stress. The offset fluctuation causes deterioration of detection accuracy. The present disclosure provides a device configuration that is as simple as possible and capable of appropriately suppressing deterioration of detection accuracy due to internal stress.
An example embodiment of the present disclosure provides a pressure sensor that generates an electrical output based on a fluid pressure. The pressure sensor includes a sensor chip and a support member. The sensor chip has a diaphragm and an inner space. The diaphragm has a thin plate shape and is bent in a thickness direction by the fluid pressure. The thickness direction defines a plate thickness of the thin plate shape. The inner space is provided by a space adjacent to the diaphragm in the thickness direction. The support member supports the sensor chip at a position separated from the diaphragm. A distance between a joint surface and a gauge surface is defined as h. The joint surface is one surface of the sensor chip, which is orthogonal to the thickness direction, and is joined to the support member. The gauge surface is another surface of the sensor chip, which is orthogonal to the thickness direction, and an opposite surface of the joint surface. When the sensor chip is viewed along the thickness direction, a diameter of an inscribed circle in case where an outer shape of the sensor chip is provided by a polygonal shape or a diameter in case where the outer shape of the sensor chip is provided by a circular shape is defined as d1. The plate thickness of the diaphragm is defined as t. When the diaphragm is viewed along the thickness direction, a diameter of an inscribed circle in case where an outer shape of the diaphragm is provided by a polygonal shape or a diameter in case where the outer shape of the diaphragm is provided by a circular shape is defined as d2.
h satisfies h=0.3 to 2.5 mm.
d1 satisfies d1=0.7 to 2.5 mm.
h/d1 satisfies h/d1≥1.
t satisfies t=5 to 15 μm.
d2 satisfies d2=350 to 700 μm.
An example embodiment of the present disclosure provides a pressure sensor that generates an electrical output based on a fluid pressure. The pressure sensor includes a sensor chip and a support member. The sensor chip has a diaphragm and a frame. The diaphragm has a thin plate shape and is bent in a thickness direction by the fluid pressure. The thickness direction defines a plate thickness of the thin plate shape. The frame is connected to an outer edge of the diaphragm to support the diaphragm. The support member supports the sensor chip at a position separated from the diaphragm. A distance between a joint surface and a gauge surface is defined as h. The joint surface is one surface of the sensor chip, which is orthogonal to the thickness direction, and is joined to the support member. The gauge surface is another surface of the sensor chip, which is orthogonal to the thickness direction, and an opposite surface of the joint surface. When the sensor chip is viewed along the thickness direction, a diameter of an inscribed circle in case where an outer shape of the sensor chip is provided by a polygonal shape or a diameter in case where the outer shape of the sensor chip is provided by a circular shape is defined as d1. The plate thickness of the diaphragm is defined as t. When the diaphragm is viewed along the thickness direction, a diameter of an inscribed circle in case where an outer shape of the diaphragm is provided by a polygonal shape or a diameter in case where the outer shape of the diaphragm is provided by a circular shape is defined as d2. When the frame is viewed along the thickness direction, a width of the frame is defined as f.
h satisfies h=0.3 to 2.5 mm.
d1 satisfies d1=0.7 to 2.5 mm.
t satisfies t=5 to 15 μm.
d2 satisfies d2=350 to 700 μm.
f satisfies f=(d1−d2)/2.
When an xy rectangular coordinate system, which is defined by x=h/d1 and y=f/d1, is set, coordinates (x, y) is within an area connecting the coordinates (1.43, 0.05), (1.43, 0.36), (1, 0.36), (0.68, 0.33), (0.56, 0.3), (1, 0.08), and (1.43, 0.05) in a described order.
Internal stress such as attaching stress may occur at the joint portion between the joint surface of the sensor chip and the support member. In an example embodiment of the present disclosure, offset fluctuation of the sensor output due to the transmission of the internal stress to the diaphragm can be suppressed as much as possible. Thus, the device configuration can be as simple as possible and appropriately suppress deterioration of detection accuracy due to internal stress.
Hereinafter, an embodiment will be described with reference to the drawings. In addition, in the following embodiments and modifications, the same reference numerals are given to the same or equivalent parts. In this case, in the following embodiments or modifications, the description in the preceding embodiment can be appropriately incorporated without technical contradiction or any special additional explanation.
With reference to
The pressure sensor 1 includes a sensor chip 2, a support member 3, and a joining layer 4. The support member 3 supports the sensor chip 2, and is provided by a metal lead frame, a ceramic substrate, a synthetic resin case, or the like. The support member 3 is arranged to face the sensor chip 2 with the joining layer 4 interposed therebetween. The joining layer 4 is made of a synthetic resin such as an epoxy resin. That is, the sensor chip 2 is joined to the support member 3 by the joining layer 4.
In the present embodiment, the sensor chip 2 has a rectangular parallelepiped shape. A joint surface 20a, which is one surface (that is, the bottom surface) of the sensor chip 2 and faces the support member 3, is joined to the support member 3 via the joining layer 4. A gauge surface 20b, which is the other surface (that is, the top surface) of the sensor chip 2, is provided opposite to the joint surface 20a so as to receive the fluid pressure.
The sensor chip 2 has a lower layer 21 and an upper layer 22. The lower layer 21 is disposed between the support member 3 and the upper layer 22. That is, the lower layer 21 has the above-described joint surface 20a. In the present embodiment, the lower layer 21 is provided by a silicon semiconductor layer having a (100) plane orientation. The upper layer 22 is joined to a surface of the lower layer 21 opposite to the joint surface 20a. That is, the upper layer 22 is disposed between the fluid which is the target of the absolute pressure measurement and the lower layer 21.
In the present embodiment, the upper layer 22 has a first semiconductor layer 22a, a second semiconductor layer 22b, and an intermediate oxide film 22c. The first semiconductor layer 22a is provided by a silicon semiconductor layer having a (110) plane orientation, and is separated from the lower layer 21. That is, the first semiconductor layer 22a has the above-described gauge surface 20b.
The second semiconductor layer 22b is provided by a silicon semiconductor layer having the (110) plane orientation, and is disposed between the lower layer 21 and the first semiconductor layer 22a. The intermediate oxide film 22c is provided by a silicon oxide film, and disposed between the first semiconductor layer 22a and the second semiconductor layer 22b. That is, the upper layer 22 is provided by an SOI layer having a stacked structure in which the first semiconductor layer 22a, the intermediate oxide film 22c, and the second semiconductor layer 22b are stacked and joined in the described order.
The sensor chip 2 has a diaphragm 23 and an internal space 24. The diaphragm 23 has a thin plate shape and is bent in the thickness direction by the fluid pressure. The “thickness direction” is the direction defining the plate thickness of the thin plate shape of the diaphragm 23, and is the direction orthogonal to the joint surface 20a and the gauge surface 20b. That is, the “thickness direction” corresponds to the vertical direction in
In the sensor chip 2, the diaphragm 23 is arranged at a position apart from the support member 3. That is, the sensor chip 2 is supported by the support member 3 at a position apart from the diaphragm 23. Specifically, the diaphragm 23 receives the fluid pressure from the space outside the pressure sensor 1 on the gauge surface 20b.
As shown in
In the present embodiment, the internal space 24 is formed as an airtight space provided inside the sensor chip 2. Specifically, a recess 25, which corresponds to the internal space 24, is formed in the second semiconductor layer 22b. The recess 25 is provided in the second semiconductor layer 22b so as to open at least to the lower layer 21. As an example, the recess 25 may be formed to penetrate the second semiconductor layer 22b in the thickness direction. In this case, the diaphragm 23 is formed in the first semiconductor layer 22a and the intermediate oxide film 22c by a portion facing the internal space 24. That is, in this case, the thickness of the diaphragm 23 corresponds to the sum of the thickness of the first semiconductor layer 22a and the thickness of the intermediate oxide film 22c.
In the present embodiment, by the lower layer 21 joined to the upper layer 22, the inner space 24 is formed as the airtight space with the recess 25 closed by the lower layer 21. In the sensor chip 2, the diaphragm 23 is bent and deformed based on the difference between the internal pressure of the internal space 24 constituting the reference pressure chamber and the pressure of the space outside the diaphragm 23. In the second semiconductor layer 22b, a frame 26, which is a portion around the inner space 24, is connected to the outer surface of the diaphragm 23 so as to support the diaphragm 23.
The diaphragm 23 is provided with a plurality of gauge resistor 27. The gauge resistor 27 is provided by a piezoresistance element in which a resistance change occurs based on distortion. The gauge resistor 27 is formed by performing impurity diffusion on the first semiconductor layer 22a. As shown in
One of the four gauge resistors 27, that is, the uppermost gauge resistor 27 in
Another one of the four gauge resistors 27, that is, the leftmost gauge resistor 27 in
The sensor chip 2 of the present embodiment satisfies the following numerical expressions. In the following numerical expressions, the thickness of the sensor chip 2 is represented by h. The distance between the opposite sides of the sensor chip 2 in the plan view is represented by d1, and d1 corresponds to the inscribed circle diameter of the sensor chip 2. The thickness of the diaphragm 23 is represented by t. The short side length of the rectangular diaphragm 23 in the plan view is represented by d2, and d2 corresponds to the inscribed circle diameter of the rectangular diaphragm 23.
h=0.3 to 2.5 mm
d1=0.7 to 2.5 mm
h/d1≥1
t=5 to 15 μm
d2=350 to 700 μm
The sensor chip 2 having the structure described above can be manufactured as follows. As described above, details of the protective film, the conductive thin film for wiring, and the like which are normally provided in the sensor chip 2 are omitted.
First, the SOI substrate which is a stacked body of the first semiconductor layer 22a, the intermediate oxide film 22c, and the second semiconductor layer 22b is prepared. Next, a gauge resistor 27 is formed on this SOI substrate. Further, the diaphragm 23 is formed in the SOI substrate by forming the recess 25 from the second semiconductor layer 22b.
In the forming of the recess 25, that is, the diaphragm 23, the anisotropic dry etching may be employed. The reasons are described as follows. Regarding the anisotropic dry etching, the etching rate of the intermediate oxide film 22c, which is provided by a silicon oxide film, is lower than the etching rate of the second semiconductor layer 22b, which is provided by the silicon semiconductor layer. Thus, the intermediate oxide film 22c functions as an etch stop layer, so that the diaphragm 23 is formed with good processing accuracy. Specifically, the thickness of the diaphragm 23 can be set with good accuracy.
The upper layer 22 is formed as described above. Thereafter, the lower layer 21 is joined to the upper layer 22 so as that the lower layer 21 makes the recess 25 airtight. Thereby, the sensor chip 2 having the airtight internal space 24 is formed.
Internal stress such as attaching stress may occur at the joint portion between the joint surface 20a of the sensor chip 2 and the support member 3. In the present embodiment, the sensor chip 2 satisfies h=0.3 to 2.5 mm, d1=0.7 to 2.5 mm, h/d1≥1, t=5 to 15 μm, d2=350 to 700 μm.
In such a configuration, the transmission of the internal stress generated at the above-described joint portion to the diaphragm 23 can be appropriately relieved by the lower layer 21. According to such a configuration, offset fluctuation of the sensor output due to the transmission of the internal stress to the diaphragm 23 can be suppressed as much as possible. Thus, with the present embodiment, the device can be as simple as possible, and the device makes it possible to appropriately suppress the deterioration of the detection precision due to the internal stress. Specifically, the influence of internal stress can be appropriately reduced without complicating the structure of the sensor chip 2 or increasing in size of the sensor chip 2.
In the present embodiment, the sensor chip 2 is mainly formed by the silicon semiconductor layer having the (110) plane orientation. Further, the diaphragm 23 has a regular octagonal shape in the plan view. Further, the two gauge resistors 27 are arranged in the vicinity of the center of the diaphragm 23 and the other two gauge resistors 27 are arranged in the vicinity of the outer surface of the diaphragm 23. With this configuration, the offset fluctuation of the sensor output can be more appropriately suppressed.
When h≥1 mm is satisfied in case of/d1≤1 mm, h/d1≥1 is satisfied. Thus, the sensor chip 2 can be formed, for example, by joining the lower layer 21 provided by a standard silicon wafer having a thickness of about 0.7 mm to the upper layer 22 in which the thickness is adjusted to 0.3 mm by polishing. Specifically, the lower layer 21 is formed using a silicon wafer having a wafer diameter of 200 mm and a thickness of 725±20 μm manufactured according to the SEMI standard, for example, SEMI stands for Semiconductor Equipment and Materials International. Thus, with this specific example, it is possible to achieve the device configuration that can appropriately suppress deterioration in detection accuracy due to internal stress without requiring a special processing such as wafer thickness adjustment to satisfy the condition of h/d1≥1.
The “offset amount (% FS)” on the vertical axis in
offset amount(unit: % FS)=100×(σn/σs)
In
In
In
The sensor chip 2 of the present embodiment further satisfies the following numerical expressions on the premise of the configuration shown in
h=0.3 to 2.5 mm
d1=0.7 to 2.5 mm
t=5 to 15 μm
d2=350 to 700 μm
f=(d1−d2)/2
The sensor chip 2 of the present embodiment satisfies the following condition.
“When the xy rectangular coordinate system, which is defined by x=h/d1 and y=f/d1, is considered, the coordinates (x, y) is within the area connecting the coordinates (1.43, 0.05), (1.43, 0.36), (1, 0.36), (0.68, 0.33), (0.56, 0.3), (1, 0.08), and (1.43, 0.05) in the described order.”
The cross marks among the multiple plots in
As is apparent from the simulation results of
(Modification)
The present disclosure is not limited to the embodiment described above and may be appropriately modified. Representative modifications will be described below. In the following description of variation examples, only the features different from those of the embodiments described above will be explained. Therefore, descriptions of previous embodiments can be referred to as required with respect to constituent elements given the same reference numerals as those of the embodiments described above in the following description of variation examples, unless there are technical contradictions or otherwise additionally described.
In the above-described embodiment, the concept of the vertical direction such as “bottom surface”, “top surface”, “lower layer 21”, “upper layer 22” and the like are merely set for convenience of explanation. That is, the attitude of the pressure sensor 1 in
The outer shape of the sensor chip 2 in the plan view is not limited to a rectangular shape. When the outer shape of the sensor chip 2 in the plan view is provided by rectangular shape, the short side length corresponds to d1. When the outer shape of the sensor chip 2 in the plan view is provided by a polygonal shape other than the rectangle shape, the inscribed circle diameter corresponds to d1. When the outer shape of the sensor chip 2 in the plan view is provided by a circular shape, the diameter corresponds to d1.
The composition of the semiconductor constituting the lower layer 21 and the upper layer 22 is also not particularly limited. The lower layer 21 may be provided by a silicon semiconductor substrate or a glass substrate.
In the above-described embodiment, the thickness of the diaphragm 23 corresponds to the sum of the thickness of the first semiconductor layer 22a and the thickness of the intermediate oxide film 22c. The present disclosure is not limited to this specific example. That is, for example, it is possible to form the recess 25 so as not to penetrate the second semiconductor layer 22b in the thickness direction. In this case, the thickness of the remaining portion of the second semiconductor layer 22b where the recess 25 is formed is added to the thickness of the diaphragm 23.
The plane shape of the diaphragm 23 can also be appropriately changed. Specifically, for example, as shown in
That is, for example, the sensor chip 2 is mainly provided by a silicon semiconductor layer having the (110) plane orientation, and the diaphragm 23 can be provided by a quadrangular shape in the plan view. In this case, d2 corresponds to the inscribed circle diameter in the rectangular shape or the short side length in the rectangular shape. In this case, the diaphragm 23 can be formed at low cost and with high accuracy using alkali anisotropic etching.
Alternatively, for example, as shown in
The internal space 24 is not limited to the airtight space. As shown in
The pressure sensor 1 having such a configuration outputs a voltage corresponding to the pressure difference on both sides of the diaphragm 23, that is, on the upper side and the lower side of the diaphragm 23 in
The configuration of the upper layer 22 is not limited to the SOI layer as described in the above-described embodiment. Specifically, as shown in
The plane orientation in each semiconductor layer is also not particularly limited. For example, the plane orientation of the first semiconductor layer 22a is not limited to (110). The second semiconductor layer 22b may have the (110) plane orientation, the (100) plane orientation, or the (111) plane orientation. Similarly to the first semiconductor layer 22a and the second semiconductor layer 22b, the lower layer 21 may have the (110) plane orientation or the (111) plane orientation. Specifically, for example, each of the lower layer 21 the first semiconductor layer 22a, and the second semiconductor layer 22b may have the (110) plane orientation. In any of these cases, the effect of reducing the internal stress can be provided.
In each of the above-described examples, the sensor chip 2 has the stacked structure of the lower layer 21 and the upper layer 22. The present disclosure is not limited to this specific example. That is, as shown in
The number, arrangement, and electrical connection configuration of the gauge resistors 27 are also not limited to the above-described example.
The present disclosure is not limited to pressure sensor 1 of gauge resistance type (i.e., piezoelectric type) as described in the example above. That is, the present disclosure may also be applicable to a pressure sensor of a type different from the gauge resistance type. Further, the pressure sensor 1 is not limited to a vehicle sensor.
The fluid of which the pressure is to be measured is not limited to gas such as intake air, exhaust gas and the like. That is, liquids, gels, supercritical fluids, or the like may also be a target to be measured. Further, the fluid at the time of pressure measurement may be in a fluid state, in a stationary state, or in a state equivalent thereto. That is, the measured pressure may be a static pressure. In this specification, the term “measurement” refers to generating an electrical output based on the fluid pressure. The electrical output may include a digital signal or digital data other than the analog signal (for example, the voltage or the like). “Measurement” may also be paraphrased as “detection”.
Variation examples are not limited to the examples illustrated above. Namely, various variation examples can be combined with each other. Also, various embodiments can be combined with each other. Moreover, all or some of the variation examples described above can be combined with combinations of various embodiments as required.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-204478 | Oct 2016 | JP | national |
The present application is a continuation application of International Patent Application No. PCT/JP2017/032337 filed on Sep. 7, 2017, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2016-204478 filed on Oct. 18, 2016. The entire disclosures of all of the above applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2017/032337 | Sep 2017 | US |
| Child | 16296920 | US |
