JP2010186920A - Imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging device capable of accelerating the speed required for an in-vehicle infrared image sensor, improving the sensitivity required for a night vision monitoring image sensor and improving a dynamic range by enabling photo detection sensitivity or dynamic range with respect to near infrared rays to be improved. <P>SOLUTION: An imaging device 1 is comprised of a near infrared line sensor 2 and a near infrared reflection movable mirror 3. The near infrared line sensor 2 is configured by forming an n-type silicon area 12 in a part of a p-type silicon substrate 11 at a side of its upper surface 13, and the n-type silicon area 12 is formed along with an incidence direction of near infrared rays incident from the side of a side surface 14 of the p-type silicon substrate 11 in such a way that its length becomes several tens to several hundreds μm. A mirror driving circuit is formed between a silicon layer 24 and a silicon substrate 22 and by applying a mirror driving voltage, a movable part 24b of the silicon layer 24 is tilted obliquely downward. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image sensor that can increase the light receiving sensitivity in the near-infrared wavelength band.

  Semiconductor image sensors represented by CCDs and CMOS imagers are used in video cameras and digital cameras, and are widely used as low-cost and low-power-consumption image sensors for converting optical signals of captured images into electrical signals. It is popular. Many of them are aimed at realizing image detection characteristics similar to those of the human eye, and are mainly formed of a silicon semiconductor in order to realize visible light sensing efficiently and with high sensitivity.

  The optical signal of the captured image can be converted into an electrical signal by using the internal photoelectric effect in the semiconductor material, and the internal photoelectric effect can be converted by the band gap of the semiconductor. The wavelength of light that can be converted is determined, and in the case of a silicon semiconductor, the wavelength range from visible light to near infrared (400 nm to 1100 nm) can be detected.

  Since near-infrared light has a longer wavelength than visible light, the absorption coefficient in a silicon semiconductor is small, and the penetration length ranges from several tens of μm to several hundreds of μm. The charge generated by the internal photoelectric effect can be efficiently collected in the depletion layer region of the PN junction, but in a general semiconductor element, the PN junction is formed at a depth shallower than about several μm and deeper than that. It is difficult to form in position. For this reason, most of the incident near-infrared light excites electrons in a region deeper than the depletion layer region of the PN junction, and these electrons recombine and disappear before being collected. As a result, there arises a problem that the light receiving sensitivity is lowered in the near infrared region.

  Near-infrared light is invisible to human eyes because it has properties close to visible light, but it is used in various places as light with properties similar to visible light. For example, it is used in a vehicle-mounted device that detects a reflected light by monitoring a place that cannot be brightened by illuminating it with near infrared light, or irradiating near infrared light even in a bright place.

In addition, if high sensitivity of sensing by near infrared rays is realized, it will be possible to capture images with a short light reception time (exposure time), so it will be an indispensable technology for in-vehicle image sensors that require high-speed image acquisition. It is done.
An example of an image sensor for the purpose of increasing sensitivity in the near infrared region is described in Patent Document 1.

JP 2006-147661 A

  The present invention has been made in consideration of such circumstances, and it is possible to increase the light receiving sensitivity and dynamic range for near infrared rays, and the high speed necessary for an in-vehicle infrared image sensor and the dark place monitoring image sensor. An object of the present invention is to provide an imaging device capable of realizing the high sensitivity and high dynamic range required for the above.

  In order to solve the above-described problems, an imaging device of the present invention includes a near-infrared reflecting movable mirror section having a reflection section that reflects near-infrared light and having a mechanism that makes the near-infrared reflection direction of the reflection section variable. A near-infrared line sensor unit in which a photodiode is formed by providing an n-type silicon region on a part of the upper surface side of the p-type silicon substrate, and the near-infrared line sensor unit reflected by the reflection unit The PN junction in the photodiode has a length corresponding to at least the penetration length of the near-infrared silicon semiconductor along the near-infrared incident direction. .

  Near-infrared light reflected by the reflecting part is incident from the side surface side of the near-infrared line sensor part, and the PN junction in the photodiode corresponds to the penetration length of the near-infrared silicon semiconductor at least along the incident direction of the near-infrared light. Therefore, when near infrared rays are incident on the photodiode, charges generated by the internal photoelectric effect can be efficiently collected in the depletion layer region of the PN junction. Therefore, the light receiving sensitivity can be increased in the near-infrared wavelength band, and the optical signal of the captured image can be efficiently converted into an electric signal.

In the present invention, the near-infrared reflecting movable mirror part and the near-infrared line sensor part can be integrally formed on the same substrate.
Further, the near-infrared reflecting movable mirror part and the near-infrared line sensor part can be independently produced and bonded and fixed on the substrate.
Which of the above-described configurations can be determined by the consistency of the respective production accuracy when producing the near-infrared reflecting movable mirror part and the near-infrared line sensor part.

In the present invention, the reflective part is formed by providing a reflective film on a silicon layer, a hinge part is connected to the reflective part, and the tilt direction of the reflective part is changed by the operation of the hinge part, It can be configured such that near infrared rays incident on the near infrared line sensor unit are scanned.
The tilting direction of the reflecting part is changed by the operation of the hinge part, and the near infrared ray incident on the near infrared line sensor part is scanned, so that a two-dimensional image can be captured with a simple operation.

In the present invention, the scanning speed of the near infrared ray incident on the near infrared line sensor unit can be made variable according to the incident intensity of the near infrared ray.
If the near-infrared light amount is weak, the scanning speed can be slowed to pick up even a weak light signal with good sensitivity. Conversely, if the near-infrared light amount is strong, the scanning speed is slowed down. Therefore, it is possible to take an image with reduced sensitivity. Alternatively, if the scanning speed is increased when the near-infrared light amount is weak, and the scanning speed is decreased when the near-infrared light amount is strong, the S / N ratio increases, so that imaging with a high contrast ratio is possible.

In this invention, the said hinge part can be formed thinner than the said reflection part, or a recessed part can also be provided in a part of said hinge part.
By making the thickness of the reflection part and the hinge part in this way, the hinge part can be driven easily, the deflection of the reflection part can be prevented, and the reflection direction of the near infrared ray reflected by the reflection part Can be prevented. For this reason, the near infrared light reflected by the reflecting portion can be accurately incident on the photodiode.

  According to the present invention, it is possible to increase the light sensitivity and dynamic range for near infrared rays, so the high speed required for in-vehicle infrared image sensors and the high sensitivity and high dynamic range required for dark place monitoring image sensors. Can be realized.

It is a figure which shows the structure of 1st Embodiment of the image pick-up element of this invention. It is a figure which shows the structure of 2nd Embodiment of the image pick-up element of this invention. It is a figure which shows the detail of a near-infrared line sensor part. It is a figure which shows the 1st example of a near-infrared reflective movable mirror part. It is a figure which shows the 2nd example of a near-infrared reflective movable mirror part. It is a figure which shows the 3rd example of a near-infrared reflective movable mirror part.

Below, this invention is demonstrated based on the embodiment.
FIG. 1 shows the configuration of the first embodiment of the image sensor of the present invention.
In FIG. 1, the image pickup device 1 includes a near-infrared line sensor unit 2 and a near-infrared reflection movable mirror unit 3. In this embodiment, the near-infrared line sensor unit 2 and the near-infrared reflection movable mirror unit 3 include It is integrally formed on the same p-type silicon substrate 11.
As shown in detail in FIG. 3, the near-infrared line sensor unit 2 is formed by forming an n-type silicon region 12 in a part on the upper surface 13 side of the p-type silicon substrate 11. Is formed such that its length L is several tens of μm to several hundreds of μm along the incident direction of near infrared rays incident from the side surface 14 side of the p-type silicon substrate 11. Thus, the PN junction functions as a photodiode formed with a length of several tens of μm to several hundreds of μm along the direction of incidence of near infrared rays.

  Since the penetration depth in the near-infrared silicon semiconductor is several tens of μm to several hundreds of μm, the PN junction is formed with a length of several tens of μm to several hundreds of μm along the incident direction of the near infrared. The infrared line sensor unit 2 has a pixel circuit region over a length corresponding to the penetration depth of the near-infrared silicon semiconductor, and charges generated by the internal photoelectric effect in the depletion layer region of the PN junction. Can be collected efficiently. Therefore, the light receiving sensitivity can be increased in the near-infrared wavelength band, and the optical signal of the captured image can be efficiently converted into an electric signal.

  The width W from the side surface 14 of the p-type silicon substrate 11 to the incident-side tip 12a of the n-type silicon region 12 is several μm or less. The side surface 14 of the p-type silicon substrate 11 can be formed by scraping off a part of the p-type silicon substrate 11 or by providing a cavity in the p-type silicon substrate 11. Near-infrared light incident from the side surface 14 of the p-type silicon substrate 11 is absorbed to some extent by this portion of the p-type silicon substrate 11, so that the width W is as small as possible from the viewpoint of preventing a decrease in light intensity due to absorption. Is desirable.

The near-infrared reflecting movable mirror part 3 is formed on the p-type silicon substrate 11 at a position separated from the near-infrared line sensor part 2 and its structure will be described below.
An insulating film 21 is provided on part of the surface 20 side of the p-type silicon substrate 11, and a silicon substrate 22 is formed on the insulating film 21. An insulating film 23 is provided on a part of the silicon substrate 22, and a silicon layer 24 is formed on the insulating film 23. A metal film 25 is provided on the upper surface of the silicon layer 24.

  The silicon layer 24 includes a fixed portion 24a formed on the silicon substrate 22 through the insulating film 23, and a movable portion 24b protruding toward the gap between the near-infrared line sensor portion 2 and the near-infrared reflecting movable mirror portion 3. It is made up of. A mirror driving circuit is formed between the silicon layer 24 and the silicon substrate 22, and when the mirror driving voltage is applied, the movable portion 24b of the silicon layer 24 is inclined obliquely downward. The metal film 25 functions as a mirror that reflects near-infrared rays, and the near-infrared rays reflected by the metal film 25 are incident on the side surface 14 of the p-type silicon substrate 11 constituting the near-infrared line sensor unit 2. As the tilt angle continuously changes, the direction in which near infrared light reflected by the metal film 25 enters the side surface 14 of the p-type silicon substrate 11 changes. As a result, near infrared light incident on a photodiode formed by a PN junction between the p-type silicon substrate 11 and the n-type silicon region 12 is scanned, and a two-dimensional image can be captured.

  The sensitivity of imaging can be changed by changing the inclination speed of the movable portion 24b, that is, the mirror scanning speed. For example, if the near-infrared light amount is weak, it is possible to pick up even a weak light signal with good sensitivity by slowing the mirror scan speed. Conversely, if the near-infrared light amount is strong, It is possible to take an image with a reduced scanning speed and a reduced sensitivity. Alternatively, if the mirror scan speed is increased when the near-infrared light amount is weak, and the mirror scan speed is decreased when the near-infrared light amount is strong, the SN ratio increases, so that imaging with a high contrast ratio is possible.

FIG. 2 shows the configuration of the second embodiment of the image sensor of the present invention.
In FIG. 2, the imaging device 1 includes a near-infrared line sensor unit 2 and a near-infrared reflecting movable mirror unit 3. In this embodiment, the near-infrared line sensor unit 2 and the near-infrared reflecting movable mirror unit 3 are They are formed on separate and independent p-type silicon substrates 11 and bonded onto the same substrate 10 by a mounting technique.

Also in this embodiment, the structures and functions of the near-infrared line sensor unit 2 and the near-infrared reflecting movable mirror unit 3 are the same as those in the first embodiment.
In the imaging device of the present invention, the configuration of the first embodiment or the configuration of the second embodiment can be appropriately selected, but the near-infrared line sensor unit 2 is manufactured using a semiconductor process technology. In addition, since the near-infrared reflecting movable mirror section 3 is manufactured using the MEMS technology, it can be selected according to the accuracy of both.

  In general, the manufacturing process is different between the semiconductor process technology and the MEMS technology. Therefore, when it is difficult to achieve accuracy matching, the near-infrared line sensor unit 2 and the near-infrared reflecting movable mirror unit 3 are connected to each other. It is convenient to adopt the configuration of the second embodiment in which the second embodiment is formed on a separate and independent p-type silicon substrate 11 and bonded on the same substrate 10 by a mounting technique. On the other hand, when it is easy to achieve accuracy matching, the near-infrared line sensor unit 2 and the near-infrared reflective movable mirror unit 3 are integrally formed on the same p-type silicon substrate 11 in the first embodiment. Convenient to configure.

In FIG. 4, the 1st example of the near-infrared reflective movable mirror part 3 is shown. 4A is a plan view of the near-infrared reflecting movable mirror section 3, and FIG. 4B is a cross-sectional view taken along the line AA.
The lamination of the p-type silicon substrate 11, the insulating film 21, the silicon substrate 22, the insulating film 23, and the silicon layer 24 is as described with reference to FIG. 1, and the electrode 26 is formed on the fixing portion 24 a of the silicon layer 24. Has been. The movable portion 24b of the silicon layer 24 includes a reflection mirror 27 that functions as a reflection portion that reflects near infrared rays, and a hinge portion 28 that is operated by a mirror driving circuit. The hinge portion 28 reflects the fixed portion 24a and the reflection portion. The mirror 27 is connected. When a mirror driving voltage is applied by the electrode 26, the hinge portion 28 is inclined obliquely downward as shown in FIG. 1, and the reflection mirror 27 is inclined obliquely downward along with this.

FIG. 5 shows a second example of the near-infrared reflecting movable mirror section 3, FIG. 5 (a) is a plan view of the near-infrared reflecting movable mirror section 3, and FIG. FIG.
The difference from that shown in FIG. 4 is that the silicon layer 24 in the portion constituting the hinge portion 28 is formed so as to be thinner than the silicon layer 24 in the other portion. Therefore, the silicon layer 24 in the portion of the reflection mirror 27 is thicker than the silicon layer 24 in the portion constituting the hinge portion 28. Since the hinge portion 28 is tilted by applying a mirror driving voltage, it is easy to drive by forming it thin. However, if the reflecting mirror 27 is also thin, both ends 27a in the longitudinal direction of the reflecting mirror 27 are It becomes easy to bend. The reflection mirror 27 has an important function of reflecting near-infrared light and causing the near-infrared ray to be incident on a photodiode formed in the near-infrared line sensor unit 2, but is reflected when the reflection mirror 27 is bent. Further, the near-infrared traveling direction is disturbed, and it becomes difficult to make the near-infrared rays accurately incident on the photodiode. Considering this, the silicon layer 24 in the part of the reflection mirror 27 is made thicker than the silicon layer 24 in the part constituting the hinge 2 part 8, thereby preventing the reflection mirror 27 from being bent. Thus, the near infrared ray reflected by the reflection mirror 27 is made to accurately enter the photodiode.

FIG. 6 shows a third example of the near-infrared reflecting movable mirror section 3, FIG. 6 (a) is a plan view of the near-infrared reflecting movable mirror section 3, and FIG. FIG.
The difference from that shown in FIG. 4 is that a concave portion 29 is provided in a part of the silicon layer 24 that constitutes the hinge portion 28. By providing the concave portion 29, the silicon layer 24 in this portion becomes thin, and it becomes easy to drive. Also in this example, like the one shown in FIG. 5, the silicon layer 24 in the portion of the reflection mirror 27 is thick, and the deflection of the reflection mirror 27 can be prevented.
5 and 6 are merely examples, and the method of forming a thin part of the silicon layer 24 that constitutes the hinge portion 28 is not limited to this.

  Since the present invention is an imaging device that increases the light receiving sensitivity with respect to near infrared rays and realizes a high dynamic range, a high-sensitivity near infrared imaging device can be configured at low cost, and high sensitivity is required. It can be used for night-vision surveillance cameras and in-vehicle cameras that require high speed.

DESCRIPTION OF SYMBOLS 1 Image sensor 2 Near-infrared line sensor part 3 Near-infrared reflective movable mirror part 10 Board | substrate
11 p-type silicon substrate 12 n-type silicon region 12a incident side tip 13 upper surface 14 side surface 20 surface 21 insulating film 22 silicon substrate 23 insulating film 24 silicon layer 24a fixed portion 24b movable portion 25 metal film 26 electrode 27 reflecting mirror 27a both ends 28 hinge Part 29 Recess

Claims (7)

  A near-infrared reflective movable mirror having a reflection part for reflecting near-infrared light and having a mechanism for changing the reflection direction of near-infrared light by the reflection part, and an n-type silicon region on a part of the upper surface side of the p-type silicon substrate A near-infrared line sensor unit having a photodiode formed thereon, and a near-infrared ray reflected by the reflecting unit is incident from a side surface side of the near-infrared line sensor unit, and a PN junction in the photodiode An imaging element having a length corresponding to at least the penetration length of a near-infrared silicon in a silicon semiconductor along an infrared incident direction.   The imaging device according to claim 1, wherein the near-infrared reflecting movable mirror part and the near-infrared line sensor part are integrally formed on the same substrate.   2. The image pickup device according to claim 1, wherein the near-infrared reflecting movable mirror part and the near-infrared line sensor part are independently manufactured and bonded and fixed on a substrate.   The reflection part is formed by providing a reflection film on a silicon layer, a hinge part is connected to the reflection part, and an inclination direction of the reflection part is changed by the operation of the hinge part, and the near infrared line sensor part The near-infrared ray which injects into is scanned, The imaging device in any one of Claim 1 to 3 characterized by the above-mentioned.   5. The imaging device according to claim 1, wherein the scanning speed of the near infrared ray incident on the near infrared line sensor unit is variable according to the incident intensity of the near infrared ray.   The imaging device according to claim 4, wherein the hinge portion is formed thinner than the reflection portion.   6. The image pickup device according to claim 4, wherein a recess is provided in a part of the hinge portion.