Patent Application
20150136984
This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2013-237277 filed on Nov. 15, 2013 in Japan, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to infrared imaging elements, imaging devices, and imaging systems.
Infrared imaging elements utilizing infrared rays are passive sensors capable of detecting the temperature distribution of objects without requiring light sources. Infrared rays pass through smoke and fog more easily than visible light rays, and infrared imaging elements may capture images during both daytime and nighttime.
On the other hand, multiple wavelength sensors capable of detecting multiple wavelengths of images at a time are being developed. Since it is possible to determine the emissivity of an object by obtaining images thereof in a plurality of wavelengths, the material and the absolute temperature of the object can be detected by using a multiple wavelength sensor. The multiple wavelength sensors may be applied to such purposes as thermography, remote sensing, or gas detection.
Multiple wavelength sensors capable of simultaneously detecting a plurality of wavelengths as described above are quantum type infrared sensors utilizing electron transition between band gaps caused by incident infrared rays. The quantum type infrared sensors should operate at low temperatures in order to prevent thermal excitation. For this reason, the quantum type infrared sensors need a cooling mechanism, which increases the costs as the size of the sensors increases.
Another method is to utilize a plurality of lenses each transmitting light of a different wavelength band to obtain images with multiple wavelengths. This method, however, requires a lens-switching mechanism, which also makes it difficult to control the size of the device and the costs.
An infrared imaging element according to an embodiment includes: a substrate having a surface in which a first recess and a second recess are provided; a first pixel portion including a first cell portion disposed above the first recess and including a first infrared ray detecting portion that detects a first infrared ray with a wavelength incident from outside and a second infrared ray with a wavelength different from the wavelength of the first infrared ray and converts the first and the second infrared rays to electrical signals, and first supporting legs that support the first cell portion to be above the first recess, the first supporting legs including a first wiring line and a second wiring line that convey the electrical signals obtained by the first infrared ray detecting portion; and a second pixel portion including a second cell portion disposed above the second recess and a second infrared ray detecting portion that detects the second infrared ray and converts the detected second infrared ray to an electrical signal, and second supporting legs that support the second cell portion to be above the second recess, the second supporting legs including a third wiring line and a fourth wiring line that convey the electrical signal obtained by the second infrared ray detecting portion.
Embodiments will now be explained with reference to the accompanying drawings.
The first pixel portions 11 and the second pixel portions 12 are alternately arranged in the row direction and the column direction. Each first wiring portion 26 is disposed between a first pixel portion 11 and a second pixel portion 12 adjacent to each other in the row direction. Each second wiring portion 27 is disposed between a first pixel portion 11 and a second pixel portion 12 adjacent to each other in the column direction.
Each first pixel portion 11 includes a first cell portion 20 and first supporting legs 21a, 21b supporting the first cell portion 20. The first supporting legs 21a, 21b include first pixel wiring lines 22a, 22b, respectively. The first cell portion 20 includes a first thermoelectric converter 23. One terminal of the first thermoelectric converter 23 is connected to the first wiring portion 26 of the corresponding column via the first pixel wiring line 22a, and the other terminal is connected to the second wiring portion 27 of the corresponding row via the first pixel wiring line 22b.
The second pixel portion 12 includes a second cell portion 30 and second supporting legs 31a, 31b supporting the second cell portion 30. The second supporting legs 31a, 31b include second pixel wiring lines 32a, 32b, respectively. The second cell portion 30 includes a second thermoelectric converter 33. One terminal of the second thermoelectric converter 33 is connected to the first wiring portion 26 of the corresponding column via the second pixel wiring line 32a, and the other end is connected to the second wiring portion 27 via the second pixel wiring line 32b.
Detailed structures of the first pixel portion 11 and the second pixel portion 12 will be described with reference to
The first cell portion 20 includes a first infrared ray absorbing portion 28 for absorbing infrared rays from the outside, and a first thermoelectric converter 23 for converting heat generated by the infrared ray absorption to electrical signals. The first infrared ray absorbing portion 28 includes a conductive layer 205, a protective film 224a for protecting the conductive layer 205, and an infrared ray absorbing layer 223a.
The first thermoelectric converter 23 is formed in the SOI layer of the SOI substrate, and includes an n+ region 200a, a p− region 201a, and a p+ region 202a to form a pn junction diode. The pn junction is formed between the n+ region 200a and the p− region 201a. The side surfaces of the first thermoelectric converter 23 are surrounded by an insulating film 222. The p− region 201a has a lower p-type impurity concentration than the p+ region 202a.
The first cell portion 20 also includes a silicide block film 204a, pixel wiring lines 22a, 22b, and silicide films 203a1, 203a2. The silicide block film 204a prevents short-circuit at the pn junction. The silicide films 203a1 and 203a2 are formed in the n+ region 200a and the p+ region 202a, respectively, and connect the pixel wiring lines 22a, 22b to the first thermoelectric converter 23 with low resistances. The following expression preferably holds:
n·L=λ/4 (1)
where L denotes the distance between the conductive layer 205 and the pixel wiring lines 22a, 22b and the distance between the conductive layer 205 and the silicide film 203a1, 203a2, n denotes the refractive index between the conductive layer 205 and the pixel wiring line 22a or 22b or silicide film 203a1, 203a2, and λ denotes a detected wavelength.
As will be described later, the first cell portion 20 is designed to absorb mid-infrared rays (2 μm to 6 μm) by causing resonance due to interference between the conductive layer 205 and the pixel wiring line 22a or 22b or the silicide film 203a1, 203a2. Therefore, from the expression (1), the distance L is preferably set in a range of 0.7 μm to 2.2 μm.
The pixel wiring line 22a extends to the corresponding first wiring portion 26, as shown in
Like the first cell portion 20, the second cell portion 30 is supported by the second supporting legs 31a, 31b above a recess 210 formed in the support substrate 220 of the SOI substrate (
The second cell portion 30 includes a second infrared ray absorbing portion 29 for absorbing infrared rays from the outside, and the second thermoelectric converter 33 for converting heat generated by the infrared ray absorption to electrical signals. The second infrared ray absorbing portion 29 includes a first infrared ray absorbing layer 224b and a second infrared ray absorbing layer 223b.
The second thermoelectric converter 33 is formed in the SOI layer of the SOI substrate, and includes an n+ region 200b, a p− region 201b, and a p+ region 202b to form a pn junction diode. The pn junction is formed between the n+ region 200b and the p− region 201b. The side surfaces of the second thermoelectric converter 33 are surrounded by the insulating film 222.
The second cell portion 30 also includes a silicide block film 204b, pixel wiring lines 32a, 32b, and silicide films 203b1, 203b2. The silicide block film 204b prevents short-circuit at the pn junction. The silicide films 203b1 and 203b2 are formed in the n+ region 200b and the p+ region 202b, respectively, and connect the pixel wiring lines 32a, 32b and the second thermoelectric converter 33 with low resistances. The pixel wiring line 32a extends to the corresponding first wiring portions 26, as shown in
The first wiring portion 26 corresponding to the first cell portion 20 includes an infrared ray absorption film 223 covering the pixel wiring line 22a formed on the insulating film 222, a via 262 formed through the infrared ray absorption film 223, a wiring layer 264 formed on the infrared ray absorption film 223 to connect to the via 262, an infrared ray absorbing layer 224 covering the wiring layer 264, and an insulating film 225 formed on the infrared ray absorbing layer 224, as shown in
The first wiring portion 26 corresponding to the second cell portion 30 includes an infrared ray absorption film 223 covering the pixel wiring line 32a formed on the insulating film 222, a via 262 formed through the infrared ray absorption film 223, a wiring layer 264 formed on the infrared ray absorption film 223 to connect to the via 262, an infrared ray absorption film 224 covering the wiring layer 264, and an insulating film 225 formed on the infrared ray absorption film 224, as shown in
The function of the infrared imaging element according to the first embodiment will be described with reference to
The mid-infrared rays 40 pass through the protective film 224a of oxide or nitride and reach the conductive layer 205. The conductive layer 205 is a semitransparent film. Part of the mid-infrared rays 40 is absorbed in or reflected on the conductive layer 205, and part thereof passes the conductive layer 205 to move in the depth direction of the first cell portion 20. The mid-infrared rays 40 also pass through the infrared ray absorbing layer 223a of oxide or nitride, and reach the pixel wiring line 22b or the silicide film 203a2. The pixel wiring line 22b and the silicide film 203a2 act as reflection films. The mid-infrared rays 40 therefore are reflected on the pixel wiring line 22b or the silicide film 203a2, pass through the infrared ray absorbing layer 223a again, and reach the conductive layer 205. Part of the mid-infrared rays 40 reaching the conductive layer 205 is reflected there. As described above, the optical distance between the conductive layer 205 and the pixel wiring line 22b or the silicide film 203a2 is designed to meet the expression (1). As a result, resonance is produced between the mid-infrared rays reflected on the silicide film 203a2 and move toward the conductive layer 205 and the mid-infrared rays incident from the outside of the first cell portion 20 to pass through the conductive layer 205 or reflected on the conductive layer 205 to move toward the silicide film 203a2 again. The mid-infrared rays thus are absorbed between the conductive layer 205 and the silicide film 203a2. The same occurs when the mid-infrared rays reaches the pixel wiring line 22a or the silicide film 203a1.
On the other hand, the far-infrared rays 41 are absorbed by the oxide film or nitride film in the first cell portion 20. Therefore, the incident far-infrared rays 41 are absorbed by the infrared ray absorbing layer 224a or the infrared ray absorbing layer 223a. Thus, both the mid-infrared rays 40 and the far-infrared rays 41 are absorbed and converted to thermal energy in the first cell portion 20. The converted thermal energy is converted to electrical signals in the thermoelectric converter 23, and conveyed to the outside via the wiring lines 22a, 22b.
Next, the function of the second pixel portion 12 will be described with reference to
The far-infrared rays 41 are absorbed by the infrared ray absorption film 224b or the infrared ray absorption film 223b to be converted into thermal energy. The converted thermal energy is converted to electrical signals at the thermoelectric converter 33, and conveyed to the outside of the second cell portion 30 via the pixel wiring lines 32a, 32b.
As described above, both the mid-infrared rays 40 and the far-infrared rays 41 of the incident electromagnetic waves are absorbed in the first cell portion 20 of the first pixel portion 11 and converted to electrical signals. In contrast, in the second pixel portion 12, the far-infrared rays 41 of the incident electromagnetic waves are absorbed in the second cell portion 30, and converted into electrical signals. As a result, first information (indicated by the solid line shown in
A method of manufacturing the infrared imaging element 10 according to the first embodiment will be described with reference to cross-sectional views shown in
First, as shown in
Next, as shown in
Then, as shown in
Subsequently, a block film 204 is formed on the surface of the semiconductor layer 206 to cover an end of the p+ region 202 on the side of the n+ region 200 to an end of the n+ region 200 on the side of the p+ region 202 (
Next, a metal film 208 to serve as pixel wiring lines 21 is formed by, for example, a sputtering method as shown in
In this manufacturing method, silicide films, the silicide film 2031 and the silicide film 2032, are formed in the first cell portion 20 and the second cell portion 30, respectively on the metal film 208 on the side of the substrate 220. This enables a low resistance connection between the metal film 208 and the thermoelectric converters 23, 33.
Next, as shown in
Next, a silicon oxide film 223 to serve as infrared ray absorbing layers 223a, 223b is formed by CVD, as shown in
Subsequently, a conductive film 205 is formed at the position where the first cell portion 20 is to be formed in the first pixel portion 11 by, for example, a sputtering method, as shown in
Next, as shown in
Subsequently, some portions of the insulating film 221, the element isolation insulating film 222, the infrared ray absorption film 223, and the infrared ray absorption film 224 are removed to form etching holes 280 so that the first and the second cell portions 20, 30 are separated from the wiring regions (
Thereafter, the surface of the support substrate 220 is etched through the etching hole 280 to form recesses 210 between the first cell portion 20 and the support substrate 220, and between the second cell portion 30 and the support substrate 220, as shown in
In the above descriptions, the process of forming the wiring layer 264 and the via 262 of the first wiring portions 26 shown in
As described above, according to the first embodiment, an infrared imaging element can be provided which is capable of detecting a plurality of wavelength bands simultaneously without switching optical lenses. The infrared imaging element according to the first embodiment detects infrared rays by thermoelectric conversion, and therefore does not need any cooling mechanism. Since no cooling mechanism is needed and no switching of optical lenses is required in the first embodiment, downsizing and low costs can be achieved.
An infrared imaging element according to a second embodiment will be described with reference to
Although the wiring layers 22a, 22b of the infrared imaging element according to the first embodiment shown in
In the first pixel portion 11 according to the second embodiment, a silicide film 203a1 on a pn junction diode is electrically connected to the wiring layer 22a through a contact layer 300a, and a silicide film 203a2 is electrically connected to the wiring layer 22b with a contact layer 300b.
Mid-infrared rays from the outside pass through the infrared ray absorbing layer 224, a part of the mid-infrared rays being reflected on the wiring layers 22a, 22b, and the rest thereof passing through the wiring layers 22a, 22b, moving toward the infrared ray absorbing layer 223, and being reflected by the silicide films 203a1, 203a2. The reflected mid-infrared rays pass through the infrared ray absorbing layer 223, reach the wiring layers 22a, 22b, and are reflected by the wiring layers 22a, 22b. As a result, as in the case of the first embodiment, resonance occurs between the mid-infrared rays passing through the wiring layers 22a, 22b and the mid-infrared rays reflected by the silicide films 203a1, 203a2 in locations between the silicide film 203a1 and the wiring layer 22a and between the silicide film 203a2 and the wiring layer 22b. The mid-infrared rays are then absorbed by the infrared ray absorbing layer 223. As described in the descriptions of the first embodiment, the optical distance between the silicide film 203a1 and the wiring layer 22a, and between the silicide film 203a2 and the wiring layer 22b is set to meet the expression (1). The far-infrared rays are absorbed by the infrared ray absorbing layer 223 and the infrared ray absorbing layer 224.
Although the basic structure of the second pixel portion 12 of the second embodiment shown in
The two wavelengths may be detected separately by setting the area in which the silicide layers faces the wiring layers disposed on the other side of the infrared ray absorbing layer 223 to be different between the first pixel portion 11 and the second pixel portion 12.
The infrared imaging element according to the second embodiment is also capable of detect multiple wavelengths simultaneously, like the infrared imaging element according to the first embodiment. Since no cooling mechanism is needed and no switching of optical lenses is required downsizing and low costs can be achieved.
By significantly differentiating the size of the thermoelectric converter 23 from the size of the thermoelectric converter 33 as in the modification, the areas of the silicide films opposing the wiring layers on the opposite side of the infrared ray absorbing layer 223 can be made different between the first pixel portion and the second pixel portion, and the same effect as the second embodiment can be obtained.
An imaging system according to a third embodiment will be described with reference to
The imaging system according to the third embodiment can be used for detecting gasoline flame. The graphs g1, g2, and g3 shown in
The infrared imaging element 10 of the imaging device 400 according to the third embodiment allows a mid-infrared image and a far-infrared image to be captured simultaneously. Images captured by the infrared imaging element 10 are processed by the signal processing unit 350 where image signals are created. Subsequently, the determination device 410 calculates a ratio between pixel values of the mid-infrared image and the far-infrared image based on the image signals obtained from the imaging device 400. As a result, characteristics of the object can be determined based on the ratio in pixel value between the mid-infrared image and the far-infrared image. The determination device 410 prestores material data corresponding to the ratio. If the captured image is determined to be gasoline flare, an alarm command signal is sent to the alarming device 420. Upon receiving the alarm command signal, the alarming device 420 provides an alarm to notify the user of the abnormal condition.
As in the case of the first embodiment, the imaging system according to the third embodiment is capable of detecting multiple wavelengths simultaneously. Furthermore, since no cooling mechanism is needed, and no switching of optical lenses is required, downsizing and low costs can be achieved.
Thus, the target material can be detected by capturing images in two wavelengths simultaneously, and performing calculation using the obtained data. The optical system of the imaging device 400 is preferably formed of a material transmitting lights in the mid-infrared range and the far-infrared range. A preferable system is basically formed of germanium or chalcogenide glass with an antireflection film formed thereon, the antireflection film being designed to transmit lights having a long wavelength in the mid-infrared range or more.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-237277 | Nov 2013 | JP | national |
