The present invention relates to a MEMS (micro electro mechanical system) sensor in a membrane structure which responds to temperature change, pressure change, vibration and the like.
Generally, there has been known a thermal sensor in a membrane structure as this kind of MEMS sensor (see Patent Document 1). The thermal sensor has a rectangular membrane formed by a thermal sensitive element and an upper and a lower electrodes, and a pair of support arms which support to release the membrane on a substrate. Each support arm serves as a wiring connected to an electrode and is formed by a thermal insulation material. The thermal sensitive element absorbs infrared rays and converts temperature change thereof to electrical signals, thereby the infrared rays can be detected.
[Patent Document 1] U.S. Pat. No. 6,087,661
In such a known thermal sensor, detection sensitivity can be improved by forming the membrane thinly and reducing thermal capacity. There arises a problem by forming the membrane thinly, in which warpage and crack occurs by stress (thermal stress, etc.) in a fabrication process, leading to an extremely low yield ratio. Further, by forming the membrane thinly, a resonance frequency is lowered. As to a sensor or the like for a vehicle, problems such that the membrane thereof is crashed by the resonance and a connection portion between the support arm and the membrane is broken and the like occur. Still further, in a case that the thermal sensitive element of the membrane is made from ferroelectric, microphonics is generated by vibration and the detection sensitivity drops off.
It is an advantage of the invention to provide a MEMS sensor which can be formed thinly while strength thereof is maintained.
According to an aspect of the invention, there is provided a MEMS sensor having a frame portion formed in a polygonal frame shape and a membrane having sensitivity as sensor that is constructed within the frame portion and that a peripheral portion thereof connected at least on an inner surface of the frame portion is formed in a plurality of convexoconcave shapes, and the MEMS sensor constituting each element of an array sensor.
According to the structure, since a connection portion of the membrane with the frame portion is formed in a convexoconcave shape, integral strength with the frame portion is improved, stress concentration of the connection portion is reduced and strength of the membrane itself can be increased. Therefore, it is possible to form the membrane thinly while a yield ratio is highly maintained. Further, a resonance frequency can be extremely raised because of the strength of the peripheral portion, thereby crack/breakage by vibration can be avoided and microphonics can not be generated.
In this case, it is preferable that length between a concave portion and a convex portion in the plurality of convexoconcave shapes in a front and back surface direction is longer than thickness of the membrane.
According to the structure, it is possible to have a boundary wall portion between the concave portion and the convex portion as rib structure having enough width, to increase strength of the membrane itself and to integrate the membrane and the frame portion closely.
Further, it is preferable that the plurality of convexoconcave shapes extend at least to two directions and concave portions and convex portions be disposed in a web shape within a whole in-plane area of the membrane.
According to the structure, it is possible to further increase the strength of the membrane itself and the membrane can be formed thinly therefor.
Further, it is preferable that the polygon be either one of a triangle, a quadrangle and a hexagon.
According to the structure, a sensor array having high rigidity can be formed in which frame portions are shared in adjacent MEMS sensors and an area ratio of the membrane (sensitive section) is high.
It is preferable that the membrane be formed by laminating an upper electrode layer, a pyroelectric layer and a lower electrode layer.
According to the structure, it is possible to provide an infrared ray sensor of which a yield ratio is high and which has high detection sensitivity.
According to the MEMS sensor of the invention, since a connection portion in the membrane with the frame portion is formed in the convexoconcave shape, the integral strength with the frame portion is improved and the strength of the membrane is improved. Further, crack/breakage by vibration can be avoided. Therefore, the yield ratio and detection sensitivity can be enhanced.
An infrared ray sensor as a MEMS sensor according to one embodiment of the invention and a sensor array using the infrared ray sensor will be explained with reference to accompanying drawings. The infrared ray sensor is fabricated by microfabrication technology with a silicon (wafer) material and the like, and is formed, as it is called, as a pyroelectric type infrared ray (far-infrared ray) sensor. Further, the infrared ray sensor forms a pixel (element) of the sensor array (infrared ray detection apparatus) fabricated in an array form.
As illustrated in
The frame portion 2 is formed in a square frame shape by deep reactive ion etching (RIE) from a front and a back (an upper and a lower) surfaces of a silicon substrate. Further, four frame pieces 2a constituting each side of the frame portion 2 have same thickness. Each side of the frame portion 2 of the embodiment is formed in size of approximately 50 μm. The frame portion is preferably formed in a polygonal shape such as a square, a rectangle, a triangle, a hexagon, etc. in consideration of strength.
Further, as illustrated in
As illustrated in
The lower electrode layer 13 is made from, for example, Au, SRO, Nb-STO, LNO (LaNiO3), etc. In this case, in consideration of film-forming of the pyroelectric layer 12 on the lower electrode layer 13, the lower electrode layer 13 is preferably made from a material having a same crystal structure as that of the pyroelectric layer 12. Further, the lower electrode layer 13 may be made from general Pt, Ir, Ti or the like. On the other hand, the upper electrode layer 11 is made from, for example, Au-Black or the like to improve absorbability of infrared rays. The upper electrode layer 11 and the lower electrode layer 13 in the embodiment are formed having approximately 0.1 μm thickness, respectively.
The membrane 3 having such a laminated structure is formed having a convexoconcave shape in a planar surface, in other words, two-dimensionally. More specifically, within a whole in-plane area of the membrane 3 where the convexoconcave shape extends to two orthogonal directions, rectangular shaped concave portions 3a and rectangular shaped convex portions 3b seen horizontally are disposed in a web shape (matrix). In other words, four convex portions 3b are adjacent to one arbitrary concave portion 3a and four concave portions 3a are adjacent to one arbitrary convex portion 3b. Therefore, as illustrated in
Further, adjacent concave portion 3a and convex portion 3b form a peripheral wall 3c in common, and the peripheral wall 3c constitutes a portion of the infrared ray detection portion and functions as reinforcement rib. A height of the peripheral wall 3c functioning as reinforcement rib, that is, length between the concave portion 3a and the convex portion 3b in a front and back surface direction is formed longer than thickness of the membrane 3. For example, in the embodiment, the length in the front and back surface direction is approximately 2.5 μm.
The reinforcement rib of the embodiment is formed at orthogonal to the in-plane direction of the membrane 3, but it may be inclined. More specifically, as illustrated in
Referring to
Then, a portion to become the membrane 3 later is film-formed by epitaxial growth (CVD) with the lower electrode layer 13, the pyroelectric layer 12 and the upper electrode layer 11 sequentially on a surface of the silicon substrate W, that is, on the oxidized film Wa (
Finally, a third etching (for example, isotropic etching by wet etching) is performed from the back surface side or from the front side by reversing the sides of the silicon substrate W to remove a substrate portion to be a lower side of the membrane 3 (
In such a structure, since the membrane 3 is formed in a convexoconcave shape, strength can be integrally improved with the frame portion 2 and strength of the membrane 3 itself can be enhanced. Therefore, breakage in a fabrication process can be avoided effectively and the membrane 3 can be formed thinly with a high yield rate. Further, a resonance frequency of the membrane 3 can be extremely raised because of the convexoconcave shape, crash/breakage by vibration can be avoided and microphonics can not be generated. Therefore, a yield rate and detection sensitivity can be enhanced simultaneously.
A modification of the first embodiment above will be explained with reference to
The infrared ray sensor 1 according to the modification in
A sensor array (infrared ray detection apparatus) 20 having the infrared ray sensors 1 of the first embodiment as sensor elements will be explained with reference to
The sensor array 20 in
In such a sensor array 20, since the frame pieces 2a in the adjacent infrared ray sensors 1 are shared (in other words, doubled), rigidity (strength) as the whole sensor array 20 can be increased and a ratio of a total area of the membranes 3 to that of the frame portions 2 can be increased, thereby a yield ratio and detection sensitivity can be improved. Further, different resonance frequencies can be applied to the adjacent infrared ray sensors 1 and the resonance frequency can be held down for the whole sensor array 20. Therefore, it is possible to avoid crash/breakage by vibration of the sensor array 20 and the sensor array 20 suitably applied in a vehicle can be formed.
The sensor array 20 in
Referring to
The membrane 33 (diaphragm 42) includes a central flat portion 33a constituting a main portion of the pressure reception portion and a convexoconcave peripheral portion 33b connecting the central flat portion 33a and the frame portion 2. In this case, the peripheral portion 33b is also formed in convexoconcave shape two-dimensionally and has a configuration in which the concave portions 3a and the convex portions 3b are disposed alternately. Thickness of the membrane 3 is determined based on a level of detected pressure.
In such a pressure sensor 31 as the first embodiment, since the peripheral portion 33a of the membrane 33 is formed in a convexoconcave shape strength is integrated with the frame portion 2 and strength of the membrane 33 is improved. Therefore, it is possible to form the membrane 33 thinly with a yield ratio. Further, it is possible to extremely raise a resonance frequency of the membrane 33 because of the convexoconcave shape, thereby crash/breakage by vibration can be avoided.
1: infrared ray sensor 2: frame portion 2a: frame piece 3: membrane 3a: concave portion 3b: convex portion 11: upper electrode layer 12: pyroelectric layer.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2009/004977 | 9/29/2009 | WO | 00 | 5/24/2012 |