Imaging device and imaging system

An imaging device includes a first substrate in which a plurality of first pixels each including a first light receiving unit and a light emitting unit that emits light with a light amount in accordance with a light amount detected by the first light receiving unit are provided, and a second substrate that is provided facing the first substrate and in which a plurality of second pixels each including a second light receiving unit that detects a light emitted from the light emitting unit of the first pixel and a readout circuit that outputs an image signal based on information detected by the plurality of second pixels are provided.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an imaging device and an imaging system.

Description of the Related Art

As an imaging device that acquires an image of a wavelength band above 1.0 μm, Japanese Patent Application Laid-Open No. H05-335375 discloses an imaging device having a configuration in which a first substrate provided with a photodiode array and a second substrate provided with a functional element used for performing signal processing are connected to each other by metal bumps. This imaging device is manufactured by fabricating the first substrate and the second substrate by wafer processes, respectively, and then electrically and mechanically connecting the first substrate and the second substrate by using metal bumps of indium (In) or the like.

The first substrate outputs signals, and the number of signals is the same as that of photodiodes forming the photodiode array. The second substrate has a function of converting an output signal from the first substrate into an image signal and performing electrical output in accordance with the number of electrode pins that may be accommodated in a general package. Thus, with a module being formed of only the first substrate, the number of electrode pins from which signals are picked out will be numerous, which is difficult to be used as an imaging device in the actual practice. In terms of the above, not only the first substrate provided with a photodiode array but also the second substrate provided with a function element is included to form a module, and an imaging device is formed.

In the imaging device formed of the first substrate provided with a photodiode array and the second substrate provided with a functional element, however, there are various constraints in terms of performance, cost, or the like due to the connection form between the first substrate and the second substrate.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a high-performance and reliable imaging device and a high-performance and reliable imaging system that include a substrate in which a light receiving unit is provided and a substrate in which a readout circuit is provided.

According to one aspect of the present invention, there is provided an imaging device including a first substrate in which a plurality of first pixels each including a first light receiving unit and a light emitting unit that emits light with a light amount in accordance with a light amount detected by the first light receiving unit are provided, and a second substrate that is provided facing the first substrate and in which a plurality of second pixels each including a second light receiving unit that detects a light emitted from the light emitting unit of the first pixel and a readout circuit that outputs an image signal based on information detected by the plurality of second pixels are provided.

DESCRIPTION OF THE EMBODIMENTS

As described previously, there are various constraints in performance, manufacturing cost, or the like in an imaging device in a form in which a first substrate provided with a photodiode array and a second substrate provided with a functional element are connected to each other by metal bumps.

For example, when heating during connection by metal bumps, there may be a constraint in the area of a sensor unit due to the difference between the thermal expansion coefficient of the first substrate and the thermal expansion coefficient of the second substrate. A compound semiconductor substrate is typically used as the first substrate, and a silicon substrate is typically used as the second substrate. For example, when an InP substrate is used as the first substrate and a silicon substrate is used as the second substrate, with the width of the substrate being around 30 mm, a difference in a change of length due to thermal expansion will be around 20 μm for some heating conditions. Since this difference corresponds to a size corresponding to the general size of a pixel, it is difficult to achieve bump connection under such conditions.

Further, there may be a constraint in the size of a pixel. When the first substrate and the second substrate are in an ideal state where there is no warping, a low height of the metal bump does not cause any problem in joining, however, there is warping in fact to some degrees in both the substrates. When such substrates are joined, an in-plane distribution in the gap between the substrates in accordance with warping of the substrates may occur. Thus, a clearance width in accordance with a difference in the gaps is required to be provided to the height of the metal bump electrically connecting the first substrate and the second substrate to each other, and as a result, a certain height is required for the metal bump. On the other hand, there is a limit in the aspect ratio (a ratio of a lateral width and a height) of the metal bump, and the lateral width of the metal bump cannot be narrower than a limit value of the aspect ratio. As a result, the size of a pixel is restricted by the size of the metal bump and cannot be reduced to a certain size or smaller.

Further, a yield of a joining process of substrates by using the metal bump is not so high as a yield of a silicon wafer process in general. Thus, a yield of imaging devices in which the first substrate and the second substrate are connected by using the metal bump is affected by a yield of a joining process and may often be lower than a yield of imaging devices formed only of silicon and configured to acquire an image in a visible light band.

Some embodiments of the present invention that may solve the above problems will be described below. Note that the present invention is not limited to only the embodiments described below. For example, a modified example in which a part of the configuration of the embodiment described below is changed within a scope not departing from the spirit of the present invention is also one of the embodiments of the present invention. Further, a form in which a part of the configuration of any of the embodiments described below is added to another embodiment or a form in which a part of the configuration of any of the embodiments is replaced with a part of the configuration of another embodiment is one of the embodiments of the present invention.

First Embodiment

An imaging device according to a first embodiment of the present invention will be described with reference toFIG. 1toFIG. 7.FIG. 1is a perspective view illustrating the structure of an imaging device according to the present embodiment.FIG. 2AandFIG. 2Bare diagrams each illustrating one example of a plan layout of a readout circuit substrate and a sensor substrate forming the imaging device according to the present embodiment.FIG. 3is a schematic cross-sectional view illustrating the structure of the imaging device according to the present embodiment.FIG. 4is a schematic cross-sectional view illustrating the structure of the sensor substrate forming the imaging device according to the present embodiment.FIG. 5is a diagram illustrating optical connection between the readout circuit substrate and the sensor substrate forming the imaging device according to the present embodiment.FIG. 6is a diagram illustrating a track of a light passing through an optical system of a general CMOS image sensor used in a visible light band camera or the like.FIG. 7is an equivalent circuit diagram illustrating the operation of the sensor substrate forming the imaging device according to the present embodiment.

As illustrated inFIG. 1, an imaging device300according to the present embodiment has the structure in which a readout circuit substrate100and a sensor substrate200are attached to each other. The sensor substrate200is a substrate including an optical sensor used for image capturing. The readout circuit substrate100is a substrate including a readout integrated circuit (RoIC) used for outputting, as a readout image signal, information detected by an optical sensor of the sensor substrate200. The readout circuit substrate100and the sensor substrate200are attached via spacers290so as to face each other via a predetermined spacing. Between the readout circuit substrate100and the sensor substrate200, bumps170responsible for electrically connecting them are provided.

For a base material of the readout circuit substrate100, a silicon substrate for which wafer process techniques or integration techniques have been accumulated is preferably used in terms of providing a readout integration circuit. Further, the primary reason why an optical sensor is mounted on the sensor substrate200separated from the readout circuit substrate100is to use a substrate whose material is different in light absorption characteristics from a material forming the readout circuit substrate100. From such a point of view, a substrate made of a material different from silicon, for example, a compound semiconductor substrate is preferably used for a base material of the sensor substrate200. A compound semiconductor substrate may be an InP substrate, a GaAs substrate, or the like. Note that the absorption wavelength band of a material based on InGaAs, GaAsSb, AlGaInAsP, or the like that enables crystal growth over InP or GaAs substrate is in the longer wavelength side than the absorption wavelength band of a single crystalline silicon. The sensor substrate200may be one in which a compound semiconductor layer such as an InP layer is provided in a separate substrate such as a sapphire substrate. While an example in which a silicon substrate is used as the base material of the readout circuit substrate100and an InP substrate is used as the base material of the sensor substrate200will be described in the present embodiment, materials of the readout circuit substrate100and the sensor substrate200may be appropriately selected where necessary.

FIG. 2Ais a diagram illustrating one example of a plan layout of the readout circuit substrate100. As illustrated inFIG. 2A, a pixel region104in which a plurality of pixels102are arranged in a matrix and a peripheral circuit region106in which a peripheral circuit used for performing driving of the pixels102or processing of output signals from the pixels102is arranged are provided in the readout circuit substrate100. Further, pad electrodes150and152used for electrical connection to the sensor substrate200via the bumps170, and a plurality of pad electrodes154used for external electrical connection are provided on the readout circuit substrate100. The pad electrodes150and152are provided outside the pixel region104. The pad electrodes150and152are connected to the peripheral circuit via internal interconnections (not illustrated) and configured to be able to supply power to the sensor substrate200via the pad electrodes150and152and the bumps170.

FIG. 2Bis a diagram illustrating one example of a plan layout of the sensor substrate200. As illustrated inFIG. 2B, a pixel region204in which a plurality of pixels202are arranged in a matrix and spacers290arranged so as to surround the pixel region204are provided in the sensor substrate200. Further, a pad electrode270electrically connected to a common electrode262arranged so as to surround the pixel region204and a pad electrode272electrically connected to ring electrodes260of respective pixels202are provided in the sensor substrate200. The pad electrodes270and272are provided outside the pixel region204. The plurality of pixels202are arranged so as to face the plurality of pixels102arranged in the pixel region104of the readout circuit substrate100, respectively, when the readout circuit substrate100and the sensor substrate200are attached to each other. Further, the pad electrodes270and272are arranged so as to face the pad electrodes150and152arranged in the readout circuit substrate100, respectively, when the readout circuit substrate100and the sensor substrate200are attached to each other.

FIG. 3is a schematic cross-sectional view taken along a line A-A′ ofFIG. 2AandFIG. 2Bafter the readout circuit substrate100and the sensor substrate200are attached to each other.

The readout circuit substrate100includes a silicon substrate110as the base material. The pixel region104and the peripheral circuit region106described previously are provided in the silicon substrate110.FIG. 3illustrates three pixels102arranged in the pixel region104and one peripheral transistor MP arranged in the peripheral circuit region106. In the actual implementation, the plurality of pixels102are arranged in a matrix in the pixel region104. Further, a plurality of peripheral transistors MP including those having the opposite conductivity type in the peripheral circuit region106are arranged. Note that while a case where signal charges are electrons will be described below as an example, signal charges may be holes. When signal charges are holes, the conductivity type of each semiconductor region will be the opposite conductivity type.

Each of the pixels102includes a light receiving unit116, a floating diffusion (hereafter, referred to as “FD”), a transfer transistor M1, a first lens162, and a second lens166. Note that the pixel102may include an in-pixel readout circuit including an amplifier transistor, a reset transistor, a select transistor, or the like as with a general CMOS image sensor.

Each light receiving unit116is a photodiode including an n-type semiconductor region114and a p-type semiconductor region115provided inside the silicon substrate110. Signal charges generated by photoelectric conversion inside the silicon substrate110are collected in the n-type semiconductor region114. The p-type semiconductor region115is arranged so as to be in contact with a primary face112of the silicon substrate110. The photodiode forming the light receiving unit116is a so-called buried photodiode.

Each FD is formed of an n-type semiconductor region118provided inside the silicon substrate110. Each transfer transistor M1includes a gate electrode128provided via a gate insulating film124over the silicon substrate110between the n-type semiconductor region114and the n-type semiconductor region118. The transfer transistor M1has a function of transferring signal charges generated by the light receiving unit116and accumulated in the n-type semiconductor region114to the FD. The signal charges transferred to the FD are converted by a capacitance component of the FD into a voltage in accordance with an amount of signal charges transferred from the light receiving unit116. The FD is electrically connected to the input node of an amplifier unit (not illustrated). The amplifier unit may be arranged in each pixel. Alternatively, the FD is electrically connected to a signal output line (not illustrated).

The peripheral transistor MP includes n-type semiconductor regions120and122as source/drain regions provided inside the silicon substrate110and a gate electrode130provided over a silicon substrate110between the n-type semiconductor regions120and122with a gate insulating film126interposed therebetween.

An insulating layer140is provided in the silicon substrate110. The insulating layer140may be formed of silicon oxide, for example. A first interconnection layer142and a second interconnection layer144are provided inside the insulating layer140. A third interconnection layer146is provided in the insulating layer140. The first interconnection layer142, the second interconnection layer144, and the third interconnection layer146are arranged at different levels with respect to the primary face112of the silicon substrate110. The first interconnection layer142and the second interconnection layer144are formed of conductive members whose primary material is copper, for example. The third interconnection layer146is formed of a conductive member whose primary material is aluminum, for example. The pad electrodes150,152, and154may be formed of the third interconnection layer146.

The conductive member of a part of the first interconnection layer142and the conductive member of a part of the second interconnection layer144are electrically connected by a via plug (not illustrated). The conductive member of a part of the second interconnection layer144and the conductive member of a part of the third interconnection layer146are electrically connected by a via plug (not illustrated). The via plug may be formed of a conductive material such as tungsten, for example. The conductive member of the first interconnection layer142, the conductive member of the second interconnection layer144, and the conductive member of the third interconnection layer146are insulated from each other by the insulating layer140except for portions electrically connected by via plugs. In this example, the third interconnection layer146of these interconnection layers is the most distant interconnection layer from the silicon substrate110.

Note that the insulating layer140is not necessarily required to be formed of a single type of insulating material but may be formed of a stacked member of multiple insulating layers including different materials. For example, the insulating layer140may include an anti-reflection film that prevents reflection at the surface of the silicon substrate110, a diffusion prevention film that prevents diffusion of a conductive member, an etching stopper film, or the like.

Further, the number of interconnection layers is not limited to three. Further, the conductive members forming the first interconnection layer142, the second interconnection layer144, and the third interconnection layer146are also not limited to the example described above, and the first interconnection layer142and the second interconnection layer144may be formed of conductive members whose primary material is aluminum, for example.

An insulating layer160is provided over the insulating layer140in which the third interconnection layer146is provided. The insulating layer160may function as a protection film. First lenses162are arranged for the corresponding pixels102over the insulating layer160. The insulating layer160and the first lenses162may be formed of silicon nitride, for example. In such a case, each refractive index of the member forming the insulating layer160and the member forming the first lenses162is higher than the refractive index of the member forming the insulating layer140. Note that the refractive index of the member forming the insulating layer160may be different from the refractive index of the member forming the insulating layer140. Further, the insulating layer160and the first lenses162may not necessarily be provided. Moreover, a planarization film164and second lenses166may be further provided over the first lenses162.

The sensor substrate200includes an InP substrate210as the base material. The pixel region204described previously is provided in the InP substrate210. A common layer212made of p-type InP, for example, is provided over the InP substrate210. The plurality of pixels202each made of a mesa structure including a light receiving unit220, a light emitting unit230, and the ring electrode260are provided over the common layer212. The common layer212may be a part of the semiconductor layer forming the light receiving units220. A protection film280is provided over a sidewall part of the mesa structure. An anti-reflection film214is provided over the backside of the InP substrate210.

The ring electrodes260of the plurality of pixels202forming the pixel region204and the pad electrode272are electrically connected to each other, as illustrated inFIG. 2B. Further, the light receiving units220of the plurality of pixels202forming the pixel region204are connected to the common layer212and then electrically connected to the pad electrode270via the common electrode262used for providing electrical contact to the common layer212. That is, except for a voltage drop at the common electrode262, the mesa structure of the plurality of pixels202is designed such that substantially the same voltage is applied thereto through the ring electrodes260and the common electrode262.

The layer arrangement illustrated inFIG. 4may be applied to the more specific structure of the sensor substrate200, for example. Note that the top and bottom ofFIG. 4are opposite to those ofFIG. 3for the purpose of illustrating respective layers in the order of crystal growth over the InP substrate210.

The common layer212connected to the light receiving units220of respective pixels202is provided over the primary face of the InP substrate210having a thickness of around 500 μm. The common layer212is formed of a p-type InP layer having a thickness of 3 μm, for example. An undoped InGaAs layer222having a thickness of 4 μm and an n-type InP layer224having a thickness of 1 μm are stacked in this order over the common layer212. The common layer212, the undoped InGaAs layer222, and the n-type InP layer224form the light receiving units220described above, and the undoped InGaAs layer222functions as a light receiving layer. The light receiving layer made of InGaAs has an absorption wavelength band in an infrared wavelength band. An n-type InP layer232having a thickness of 4 μm, an undoped InP layer234, and a p-type InP layer236are stacked in this order over the n-type InP layer224. The n-type InP layer232, the undoped InP layer234, and the p-type InP layer236form the light emitting units230described above, and the undoped InP layer234functions as a light emitting layer. The emission center wavelength of the light emitting unit230in which a light emitting layer is formed of InP is around 920 nm. The ring electrodes260are provided over the p-type InP layer236via an InGaAs contact layer (not illustrated). The ring electrodes260provided over the light emitting units230of respective pixels202are electrically connected to each other as described previously and are at substantially the same electrical potential except for a voltage drop due to an electrical resistance of interconnections connecting them.

As illustrated inFIG. 3, the readout circuit substrate100and the sensor substrate200are arranged such that the primary faces thereof face each other and in parallel. The plurality of pixels102of the readout circuit substrate100and the plurality of pixels202of the sensor substrate200are arranged at the same pitch so as to form respective pairs. The light receiving unit116of the pixel102and the light emitting unit230of the pixel202which form a pair are optically connected via the first lens162and the second lens166.

As discussed above, the imaging device according to the present embodiment includes the light emitting units230in the sensor substrate200on which a sensor element for image capturing (the light receiving units220) is provided and the light receiving units116in the readout circuit substrate100on which an RoIC is provided. Further, a light emitted from the light emitting unit230provided in the sensor substrate200is detected by the light receiving unit116provided in the readout circuit substrate100. Thus, by causing the light emitting unit230to emit light in accordance with the amount of light received by the light receiving unit220and detecting it by the light receiving unit116, it is possible to transmit information detected by the light receiving unit220to the readout circuit substrate100. That is, the imaging device according to the present embodiment is not configured such that the pixels102provided in the readout circuit substrate100and the pixels202provided in the sensor substrate200are electrically connected via metal bumps.

FIG. 5is a diagram illustrating optical connection between the readout circuit substrate100and the sensor substrate200. In the imaging device of the present embodiment, one lens group is formed of the first lens162and the second lens166, and a light400emitted from the light emitting unit230of the sensor substrate200is captured as an image on the light receiving unit116of the readout circuit substrate100through such a lens group.

In the imaging device of the present embodiment, an optical system is designed based on a relationship of Equation (1) below in accordance with a so-called lens formula.
1/f=1/d1+1/d2(1)

Here, the variable d1denotes an optical distance from the interface between the second lens166and the air to the light receiving unit116. The variable d2denotes an optical distance from the interface between the second lens166and the air to the light emitting unit230. The variable f denotes an effective focal length of the lens group. Note that an optical distance is represented as a product of a refractive index of a substance where a light propagates and a physical distance where a light propagates through the substance.

For comparison,FIG. 6illustrates one example of a track of a light402passing through an optical system of a general CMOS image sensor used in a camera or the like having a sensitivity in a visible light band. As illustrated inFIG. 6, an optical system of a general CMOS image sensor is configured to converge a light that is closer to a parallel light than in the case of an optical system of the present embodiment into the light receiving unit116. That is, in a general CMOS image sensor, unlike the imaging device according to the present embodiment, an optical system is designed based on a relationship of Equation (2) below.
f=d1(2)

Next, in the imaging device according to the present embodiment, the principle by which the light receiving unit220of the sensor substrate200transmits a detected image to the readout circuit substrate100will be described.

FIG. 7is an equivalent circuit diagram illustrating the operation of the sensor substrate200. InFIG. 7, a photodiode D1corresponds to the light receiving unit220ofFIG. 3, and a light emitting diode D2corresponds to the light emitting unit230ofFIG. 3. Note that, inFIG. 7, an interconnection connected between the ring electrodes260of respective pixels202and electric resisters of the common electrode262and the common layer212are omitted.

As illustrated inFIG. 7, the photodiode D1and the light emitting diode D2forming each pixel202are connected in series such that the direction of the p-n junction is opposite to each other. Further, a DC power source180that supplies power from the readout circuit substrate100to the sensor substrate200via the pad electrodes150,152,270, and272is connected to apply a reverse bias to the photodiode D1and apply a forward bias to the light emitting diode D2. The voltage of the DC power source180is 5.0 V, for example.

With the DC power source180being connected to the series-connected circuit of the photodiode D1and the light emitting diode D2as described above, most part of the voltage supplied from the DC power source180is applied to the photodiode D1. Thereby, the photodiode D1is in a state where a sufficient reverse bias is applied, and the current flowing in the photodiode D1changes depending on the amount of a light entering the photodiode D1. Since the photodiode D1and the light emitting diode D2are connected in series, the current flowing in the light emitting diode D2is the same as the current flowing in the photodiode D1. Further, a light amount emitted from the light emitting diode D2is proportional to a current value flowing in the light emitting diode D2rather than a voltage applied to the light emitting diode D2as with a general LED. As a result, the light emitting diode D2emits light with a light amount proportional to the amount of light entering the photodiode D1.

In the imaging device according to the present embodiment, however, some degrees of a light from the light emitting unit230to the light receiving unit220is fed back due to the structure thereof. When the amount of such feedback exceeds one and becomes positive feedback, and once the light emitting unit230exceeds the threshold, the light emitting unit230will emit light regardless of an incident light amount to the light receiving unit220, and information of the light receiving unit220is unable to be transmitted to the readout circuit substrate100. Thus, the amount of a current generated by the light receiving unit220due to a light emitted from the light emitting unit230due to a current is required to be smaller than the feedback amount from the light emitting unit230to the light receiving unit220, more specifically, the amount of the current flowing into the light emitting unit230. Thus, for example, a configuration that enters two stable states by positive feedback and has an effect of a memory as disclosed in Japanese Patent Application Laid-Open No. S55-026615 is unsuitable for the configuration of the sensor substrate200of the imaging device according to the present embodiment.

In the structure illustrated inFIG. 4, the stack from the common layer212to the p-type InP layer236includes the i-layer (intrinsic layer) inserted in the middle thereof but includes the p-n-p structure as a whole. Thus, when the total film thickness of the n-type InP layers224and232is less than or equal to the thickness in which holes, which are minority carriers, can be diffused, an operation like a bipolar transistor is exhibited. When the operation like a bipolar transistor becomes significant and the amplification effect exceeds a certain level, positive feedback occurs from the light emitting unit230to the light receiving unit220, and the light emission amount at the light emitting unit230is no longer an amount in accordance with a light amount received at the light receiving unit220.

Accordingly, in the present embodiment, the total film thickness of the n-type InP layers224and232corresponding to a base layer is larger than the thickness corresponding to the diffusion length of minority carriers in order to cause the pixel202to operate stably without causing positive feedback. For example, the diffusion length of holes in the n-type InP layers224and232of the present embodiment is around 4 μm. Accordingly, in the present embodiment, the total film thickness of the n-type InP layers224and232is set to 5 μm that is thicker than the diffusion length of holes.

Note that, while the case where the diffusion length of holes is assumed to be around 4 μm here, the diffusion length of holes changes in accordance with a material or the like, and an amplification factor of a bipolar transistor changes in accordance with a doping concentration of respective layers forming a p-n junction. It is therefore desirable to adjust the total film thickness of an n-type layer appropriately in accordance with the materials forming the light receiving unit220and the light emitting unit230or the doping concentration of respective layers.

Further, diffusion of minority carriers may be blocked by inserting a layer such as AlInP, which has a larger energy band gap than that of periphery in a stack forming the light receiving unit220and the light emitting unit230, and providing a barrier on a valence band side. Further, accumulation and recoupling of carriers may be facilitated by inserting a layer having a smaller energy band gap than that of InP in order to confine minority carriers.

In the present embodiment, the InP substrate210has a thickness of around 500 μm and not significantly thinned from the initial thickness of the InP substrate210used in crystal growth of each layer. This has a purpose of absorbing a visible light in addition to facilitating handling of the sensor substrate200during manufacturing.

For example, since the absorption coefficient of InP for a light of a wavelength of 950 nm is 3×102cm−1, the InP substrate210having a thickness of around 230 μm is required for absorbing 99% of the light of a wavelength of 950 nm. Since the absorption coefficient of a light on a shorter wavelength side of the wavelength of 950 nm is much larger, with a thickness of around 230 μm or greater, a visible light can be reliably absorbed.

Next, the summary of a method of manufacturing an imaging device according to the present embodiment (step of attaching the readout circuit substrate100and the sensor substrate200to each other) will be described.

First, the readout circuit substrate100and the sensor substrate200are fabricated by a semiconductor wafer process, respectively. Then, metal bumps made of a metal material such as gold or copper are formed on the pad electrodes150and152of the readout circuit substrate100and the pad electrodes270and272of the sensor substrate200, respectively.

Next, the sensor substrate200is positioned and installed on the readout circuit substrate100, and the sensor substrate200is pressed against the readout circuit substrate100under an increased temperature. Thereby, metal bumps installed on the pad electrodes150and152and metal bumps installed on the pad electrodes270and272are subjected to thermo-compression bonding, respectively, and electrical connection between the readout circuit substrate100and the sensor substrate200is established. At this time, the spacing between the readout circuit substrate100and the sensor substrate200is defined by the height of the spacers290.

In the present embodiment, electrical connection portions between the readout circuit substrate100and the sensor substrate200are only the bumps170connected between the pad electrode150and the pad electrode270and between the pad electrode152and the pad electrode272. It is therefore possible to reduce influence on a manufacturing yield caused by a joining process of the readout circuit substrate100and the sensor substrate200and improve a connection reliability between the readout circuit substrate100and the sensor substrate200.

Next, an adhesive agent is applied to the outer circumference of the sensor substrate200by using the dispenser or the like after cooled to a room temperature, and the sensor substrate200is fixed to the readout circuit substrate100.

Note that the number or the arrangement of pad electrodes used for electrically connecting the readout circuit substrate100and the sensor substrate200to each other, the outer circumference shapes of the pixel regions104and204, the arrangement of the peripheral circuit region106, or the like may be appropriately changed if necessary. Further, a scheme of electrical connection between the readout circuit substrate100and the sensor substrate200is not limited to a form of metal bumps as long as it can supply power, and a conductive paste or the like may be used, for example. Further, a scheme of fixing the sensor substrate200to the readout circuit substrate100is not limited to an adhesive agent, and other fixing schemes may be used.

As described above, according to the present embodiment, image information captured by the sensor substrate200may be transferred to the readout circuit substrate100and electrically read out without a use of electrical connection on a pixel basis. This facilitates reduction in the pixel size or increase in the area of the sensor unit, and it is possible to realize a high-performance and reliable imaging device that can acquire an image of a long wavelength band such as above 1.0 μm.

Second Embodiment

An imaging device according to a second embodiment of the present invention will be described with reference toFIG. 8. Components similar to those of the imaging device according to the first embodiment are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 8is a schematic cross-sectional view illustrating the structure of a sensor substrate forming the imaging device according to the present embodiment.

The imaging device according to the present embodiment is the same as the imaging device according to the first embodiment except for a difference in the configuration of the light emitting unit230provided in the sensor substrate200. That is, as illustrated inFIG. 8, the pixel202of the imaging device according to the present embodiment includes the light emitting unit230in which an n-type AlInAs layer238, an undoped AlGaInAs layer240, and a p-type AlInAs layer242are stacked in this order on the light receiving unit220. The undoped AlGaInAs layer240functions as a light emitting layer.

AlGaInAs forming the undoped AlGaInAs layer240is a mixed crystal of AlAs, GaAs, and InAs and may control the energy band gap, that is, the emission center wavelength in accordance with the composition ratio thereof. Thereby, it is possible to realize a composition having a larger energy band gap than InP used in the light emitting layer of the light emitting unit230in the imaging device of the first embodiment and set the emission center wavelength to around 820 nm, for example. In such a case, since the sensitivity of a photodiode (the light receiving unit116) made of silicon is higher for a light of a wavelength of 820 nm than for a light of a wavelength of 920 nm, which is the emission center wavelength of InP, light emission of the light emitting unit230may be detected at a higher sensitivity.

Note that, while the light emitting layer of the light emitting unit230is formed of AlGaInAs in the present embodiment, the material is not particularly limited as long as it has a desired emission center wavelength and enables epitaxial growth on the base material (the InP substrate210). For example, instead of AlGaInAs, AlinAs without Ga may be used. Further, the light emitting layer may be formed of a plurality of layers or may be formed of quantum well structure. In addition, the structure used in a general LED may be introduced as the light emitting unit230.

As described above, according to the present embodiment, it is possible to realize increase in sensitivity of an imaging device in addition to obtain the same advantage as that of the first embodiment.

Third Embodiment

An imaging device according to a third embodiment of the present invention will be described with reference toFIG. 9. Components similar to those of the imaging device according to the first and second embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 9is a schematic cross-sectional view illustrating the structure of a sensor substrate forming the imaging device according to the present embodiment.

The imaging device according to the present embodiment is the same as the imaging device according to the first and second embodiments except for a difference in the configuration of the light emitting unit230provided in the sensor substrate200. That is, as illustrated inFIG. 9, the pixel202of the imaging device according to the present embodiment includes the light emitting unit230in which the n-type AlInAs layer238, the undoped AlGaInAs layer240, and an undoped AlInAs layer244are stacked in this order on the light receiving unit220. P-type regions250and252are provided in the undoped AlInAs layer244. The p-type region250is provided on the surface part of the undoped AlInAs layer244so as to be in contact with the ring electrode260. The p-type region252is provided at a deeper part than the depth of the p-type region250from the surface part of the undoped AlInAs layer244inside the undoped AlInAs layer244surrounded by the ring electrode260. In such a way, an in-plane distribution is provided in the p-type impurity added to the undoped AlInAs layer244.

With such a configuration, the current flowing in the light emitting unit230concentrates in a path which runs through the p-type region252having the narrowest width in the depth direction of the undoped AlInAs layer244and causes locally intense light emission therein. As a result, it is possible to increase the ratio at which a light is emitted in a light extraction window region surrounded by the ring electrode260and improve a light extraction efficiency.

The p-type regions250and252are not particularly limited but may be formed by adding Zn to the undoped AlGaInAs layer240by using ion implantation method, for example. At this time, it is possible to form the p-type regions250and252having different depths by changing acceleration energy of implanted ions.

Note that while an application example to the imaging device according to the second embodiment has been illustrated in the present embodiment, the same configuration may be applied to the imaging device according to the first embodiment. In such a case, the p-type InP layer236may be used as an undoped InP layer, and the same p-type regions as the p-type regions250and252may be provided in this undoped InP layer.

As described above, according to the present embodiment, it is possible to realize further increase in sensitivity of an imaging device in addition to obtain the same advantages as that of the first and second embodiments.

Fourth Embodiment

An imaging device according to a fourth embodiment of the present invention will be described with reference toFIG. 10. Components similar to those of the imaging device according to the first to third embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 10is a schematic cross-sectional view illustrating the structure of a sensor substrate forming the imaging device according to the present embodiment.

The imaging device according to the present embodiment is different from the imaging device according to the first to third embodiments in that some of the plurality of pixels202provided in the sensor substrate200each further include an individual electrode connected to the n-side terminal of the light emitting unit230.

FIG. 10illustrates an example in which the configuration described above of the present embodiment is applied to the sensor substrate200of the imaging device according to the third embodiment. That is, pixels202A which are some of the plurality of pixels202provided in the sensor substrate200each include an individual electrode264provided on the n-type AlInAs layer238that is the n-side terminal of the light emitting unit230. The individual electrode264is electrically connected to the peripheral circuit provided in the readout circuit substrate100via a wiring or a bump (not illustrated) as with the ring electrode260or the common electrode262. Thereby, the light emitting unit230of the pixel202A may cause light emission independently regardless of light incidence to the light receiving unit220by applying a voltage between the individual electrode264as an n-side electrode and the ring electrode260as a p-side electrode.

The light emitting unit230provided in the pixel202A may be used for check of alignment between the readout circuit substrate100and the sensor substrate200in addition to transfer of information to the pixel102. For example, after the readout circuit substrate100and the sensor substrate200are joined, a voltage is applied between the individual electrode264and the ring electrode260to cause light emission of the light emitting unit230of the pixel202A, and the light amount received by the light receiving unit116of the pixel102paired with the pixel202A is checked. By doing so, it is possible to check whether or not joining displacement in a direction parallel to the primary face of a substrate is within an acceptable range. This may prevent a defect whose displacement between the readout circuit substrate100and the sensor substrate200is out of the acceptable range from being delivered to a step of mounting the defect onto a ceramic package.

The location or the number of pixels202A arranged inside the pixel region204is not particularly limited. In terms of detecting two-dimensionally displacement between the readout circuit substrate100and the sensor substrate200, at least two pixels202A arranged at distant locations are needed. For example, when the pixel region204has a rectangular shape as illustrated inFIG. 2B, two to four pixels202located near the four corners of the pixel region204may be used as the pixels202A.

Displacement between the readout circuit substrate100and the sensor substrate200may be checked when the readout circuit substrate100and the sensor substrate200are joined. In such a case, the light emitting unit230of the pixel202A is caused to emit light when the readout circuit substrate100and the sensor substrate200are joined, positioning to the optimum location is performed while the amount of light received by the light receiving unit116of the pixel102paired with the pixels202A is monitored.

The advantage in such a case may be that accuracy of positioning may be higher than accuracy of mechanical positioning with a mounting apparatus. In particular, a significant advantage is obtained when a light is reduced by a lens in a configuration where the lens is used for optical connection between the light emitting unit230of the sensor substrate200and the light receiving unit116of the readout circuit substrate100or when the pixel pitch is small such as 10 micro meter or less, or the like. Note that the reason why the advantage is significant in a state where a lens is mounted is that a light is reduced to a small region by a lens and thus a change amount in a light amount resulted when displacement between the region and a light receiving unit116occurs is larger than that in a case with no lens.

In positioning by using a mounting apparatus, first, a pattern on the readout circuit substrate100and a pattern on the sensor substrate200are recognized by image recognition, and a displacement in a direction parallel to the primary face is identified. Then, the readout circuit substrate100and the sensor substrate200are moved close to each other and heated to be joined with bumps. When attachment is performed by relying only on mechanical accuracy after the displacement is identified, however, not a little displacement occurs, such as displacement from an ideal position occurs. While the problem due to the displacement is not important when the pixel pitch is relatively large, the influence due to the alignment displacement described above is no longer ignorable when the pixel pitch comes close to a usual image sensor of a visible light band formed of silicon.

Accordingly, the readout circuit substrate100and the sensor substrate200are moved close to each other by a several micro meters before coming into contact with each other, the light emitting unit230of the pixel202A is caused to emit light in such a state, and a position at which the light receiving amount is the maximum is searched for while the light receiving amount is monitored by the light receiving unit116. By doing so, since the readout circuit substrate100and the sensor substrate200may be aligned in a state of being close to each other as much as possible without a use of image recognition, displacement due to motion after alignment or the like may be significantly reduced.

Note that while an application example to the imaging device according to the third embodiment has been illustrated in the present embodiment, the same configuration may be applied to the imaging device according to the first or second embodiment.

As described above, according to the present embodiment, it is possible to improve positioning accuracy between the readout circuit substrate100and the sensor substrate200in addition to obtain the same advantages as that of the first to third embodiments. Thereby, improvement of the manufacturing yield and a further increase in the sensitivity may be realized.

Fifth Embodiment

An imaging device according to a fifth embodiment of the present invention will be described with reference toFIG. 11. Components similar to those of the imaging device according to the first to fourth embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 11is a schematic cross-sectional view illustrating the structure of the imaging device according to the present embodiment.

As illustrated inFIG. 11, the imaging device according to the present embodiment is different from the imaging devices according to the first to fourth embodiments in that lenses282provided on the light emitting units230of the sensor substrate200are further provided. The lens282has a function of shaping a light emitted from the light emitting unit230into substantially a parallel light. Further, in the imaging device according to the present embodiment, the first lens162and the second lens166provided on the readout circuit substrate100are configured to converge a parallel light404emitted from the lens282on the light receiving unit116.

In the imaging device according to the present embodiment, since the sensor substrate200side is also provided with the lens282, the number of manufacturing steps increases. In the imaging device according to the present embodiment, however, there is a specific advantage of being capable of suppressing variation in a light coupling efficiency due to variation of the spacing between the readout circuit substrate100and the sensor substrate200.

An in-plane distribution or variation may occur in the spacing between the readout circuit substrate100and the sensor substrate200due to warping, variation in the attachment step, or the like of the readout circuit substrate100and the sensor substrate200. A change in the distance between the readout circuit substrate100and the sensor substrate200causes a change in the distance between the lens group formed of the first lens162and the second lens166and the light emitting unit230. As a result, in the imaging device according to the first embodiment, displacement occurs between a position at which a light beam is converged by the lens group and a position of the surface of the light receiving unit116, which would affect a light coupling efficiency or the like between the readout circuit substrate100and the sensor substrate200.

In this regard, in the imaging device according to the present embodiment, since a light emitted from the light emitting unit230is shaped in the parallel light404by the lens282, even when the distance between the substrates changes, there is substantially no change in the position at which a light is converged inside the readout circuit substrate100. As a result, according to the imaging device of the present embodiment, it is possible to suppress a change in a light coupling efficiency due to an in-plane distribution or variation of the spacing between the readout circuit substrate100and the sensor substrate200.

As described above, according to the present embodiment, it is possible to suppress a change in a light coupling efficiency due to an in-plane distribution or variation of the spacing between the readout circuit substrate100and the sensor substrate200in addition to obtain the advantages of the first to fourth embodiments.

Sixth Embodiment

An imaging device according to a sixth embodiment of the present invention will be described with reference toFIG. 12andFIG. 13. Components similar to those of the imaging device according to the first to fifth embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 12is a schematic cross-sectional view illustrating the structure of an imaging device according to the present embodiment.FIG. 13is a graph illustrating a relationship between the distance between a readout circuit substrate and a sensor substrate and an optical coupling efficiency.

The imaging device according to the present embodiment is the same as the imaging device according to the first to fourth embodiments except that no lens group (the first lens162and the second lens166) is provided on the readout circuit substrate100. As illustrated in the present embodiment, a use of a lens group is not necessarily required for optical connection between the light emitting unit230of the pixel202provided in the sensor substrate200and the light receiving unit116of the pixel102provided in the readout circuit substrate100. There is a merit in the imaging device according to the present embodiment that manufacturing cost may be reduced by omitting the step of forming the first lenses162and the second lenses166.

FIG. 13is a graph illustrating a result obtained by calculating inter-substrate distance dependency of the light coupling efficiency between the readout circuit substrate100and the sensor substrate200in the configuration of the imaging device according to the present embodiment. The horizontal axis represents an optical distance L between the surface position of the light emitting unit230and the surface position of the light receiving unit116(seeFIG. 12). The left vertical axis represents the light coupling efficiency between the pixel202and the pixel102. The right vertical axis represents a ratio between the light coupling efficiency with respect to a right under pixel102and the light coupling efficiency with respect to another pixel102adjacent to the right under pixel102. InFIG. 13, plots with black rhombuses represents the light coupling efficiency between the pixel202and the pixel102right under the pixel202of interest. Plots with black squares represents the light coupling efficiency between the pixel202and the pixel102adjacent to the pixel102right under the pixel202of interest. Plots with black triangles represents the ratio between the light coupling efficiency with respect to the right under pixel102and the light coupling efficiency with respect to the adjacent pixel102.

In the calculation inFIG. 13, it is assumed that the pitch of the pixels102and202is 19 μm and the effective opening diameter of the light emitting unit230and the light receiving unit116is 5 μm. In the calculation, however, influence of light shielding due to members provided outside the light emitting layer of the light emitting unit230(for example, the ring electrode260or the like) is ignored.

As illustrated inFIG. 13, the light coupling efficiency between the pixel202and the pixel102increases as the spacing between the readout circuit substrate100and the sensor substrate200decreases. It is therefore possible to realize desired characteristics even with the configuration in which no lens group is provided on the readout circuit substrate100by appropriately setting the spacing between the readout circuit substrate100and the sensor substrate200in accordance with a required light coupling efficiency.

For example, it is possible to suppress the incident amount of a light to the light receiving unit116of the adjacent pixel102relative to the incident amount of a light to the light receiving unit116of the right under pixel102below around 3.5% by setting the distance L between the readout circuit substrate100and the sensor substrate200to 5 μm or less. Unlike a color-type imaging device that detects a light of a visible light band, an imaging device that detects a light of a wavelength band above 1.0 μm is a so-called monochrome imaging device that has no filters whose transmission wavelength bands are different in accordance with pixels. Thus, for some applications, even when crosstalk to an adjacent pixel is around 3.5%, this may be acceptable for usage. In such a case, with a configuration with no lens being provided as with the present embodiment, a low cost imaging device may be realized. Moreover, if crosstalk to an adjacent pixel is allowed up to around 10%, the distance L between the readout circuit substrate100and the sensor substrate200may be expanded up to around 7 μm.

Note that while an application example to the imaging device according to the first to fourth embodiments has been illustrated in the present embodiment, the same configuration as that of the present embodiment may be applied to the imaging device according to the fifth embodiment.

As described above, according to the present embodiment, it is possible to reduce manufacturing cost in addition to obtain the advantages of the first to fourth embodiments.

Seventh Embodiment

An imaging device according to a seventh embodiment of the present invention will be described with reference toFIG. 14. Components similar to those of the imaging device according to the first to sixth embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 14is a schematic cross-sectional view illustrating the structure of an imaging device according to the present embodiment.

To reduce crosstalk to an adjacent pixel as described in the sixth embodiment, it is also effective to provide a light shield wall. For example, the ring electrode260may be utilized as such a light shield wall. In the present embodiment, in the imaging device according to the sixth embodiment, an example when the ring electrode260is used as a light shield wall will be described.

Here, it is considered that the region surrounded by the ring electrode260of the light emitting unit230corresponds to an opening from which a light is emitted. Further, as illustrated inFIG. 14, the ring electrode260that is higher than that in the case of the first to sixth embodiments is assumed, and a case where a light emitted from the light emitting unit230may transmit the ring electrode260is considered. In this situation, a light beam which passes through the highest portion of the ring electrode260out of a light beam that enters the light receiving unit116of the pixel102B adjacent to the right under pixel102A emitted from the light emitting unit230of the pixel202A corresponds to a light beam408illustrated by a dotted line inFIG. 14.

Therefore, when the ring electrode260is used as a light shield wall, a light beam that enters the light receiving unit116of the pixel102B adjacent to the right under pixel102A may be effectively blocked when the height h of the ring electrode260(light shield wall) satisfies a relationship of Equation (3) below.
h>w×tan θ1  (3)

Here, the value θ1 is an angle of the light beam408relative to the surface of the light emitting unit230, and the value w is a width of the opening of the light emitting unit230(seeFIG. 14).

For example, when the width w of the opening of the light emitting unit230is 5 μm the width of the opening of the light receiving unit116is 5 μm the optical distance between the surface of the light emitting unit230and the surface of the light receiving unit116is 5 μm and the pixel pitch is 19 μm the height h of a light shield wall that satisfies the relationship described above will be 1.3 μm.

The difference from the height of the light emission face of the light emitting unit230is important for the height of a light shield wall. Thus, a member as a light shield wall is not necessarily required to be provided up to the height. For example, it is possible to realize a light shield wall having the same effect also by etching a portion of the light emitting unit230from which a light is emitted by 0.5 μm and arranging the ring electrode260having a height of 0.8 μm around the portion. Further, the light shield wall satisfying Equation (3) is not necessarily required to be the ring electrode260but may be formed by using another member. Further, a light shield wall having the same function may be provided on the readout circuit substrate100side.

As described above, according to the present embodiment, it is possible to reduce crosstalk to an adjacent pixel in addition to obtain the advantage of the sixth embodiment.

Eighth Embodiment

An imaging device according to an eighth embodiment of the present invention will be described with reference toFIG. 15. Components similar to those of the imaging device according to the first to seventh embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 15is a schematic cross-sectional view illustrating the structure of a sensor substrate forming an imaging device according to the present embodiment.

In the imaging device according to the first to seventh embodiments, each pixel202provided in the sensor substrate200is formed of a mesa structure including the light receiving unit220and the light emitting unit230. In contrast, in the imaging device according to the present embodiment, as illustrated inFIG. 15, while the light emitting unit230has the independent mesa structure for each pixel202, the undoped InGaAs layer222and the n-type InP layer224forming the light receiving unit220are not patterned for each pixel202. A p-type region226is provided in the region between the pixels202in the n-type InP layer224. The p-type region226is formed so as to surround the circumference of each pixel202in a plan view. The p-type region226is not particularly limited and may be formed by adding Zn to the n-type InP layer224by an ion implantation method, for example.

With the p-type region226being provided in the n-type InP layer224, a p-n junction may be formed at the interface between the n-type InP layer224and the p-type region226. By using a reverse direction property of this p-n junction, it is possible to electrically separate the light receiving unit220of the adjacent pixel202.

In the configuration described above of the present embodiment, since the etching depth in forming a mesa structure is smaller than that in the case of the first to seventh embodiments in which a mesa structure including the light receiving unit220and the light emitting unit230is formed, a machining process may be easier. Further, since the light receiving unit220has no mesa structure, no surface current via a mesa side wall will flow.

Further, the imaging device according to the present embodiment further includes the light shield film284between the light emitting units230of the pixels202adjacent each other. The light shield film284is not particularly limited and may be formed of a stack film of a Cr film having a thickness of 10 nm and an Au film having a thickness of 100 nm, for example.

The reason why the light shield film284is provided in the imaging device according to the present embodiment is not to cause a light generated in the light emitting unit230of one pixel202to enter the light receiving unit220(the undoped InGaAs layer222) of the adjacent pixel202. This may suppress crosstalk of light between pixels202.

The light shield film284is also applicable to the imaging devices according to the first to seventh embodiments. In the imaging devices according to the first to seventh embodiment, however, since the depth of a groove required for separating mesa structures of respective pixels202is deeper than that in the case of the present embodiment, relative difficulty in forming the light shield film284increases, as describe previously.

Note that, while an application example to the imaging device according to the third embodiment has been illustrated in the present embodiment, the same configuration as that of the present embodiment may be applied to the imaging device according to other embodiments.

As described above, according to the present embodiment, it is possible to facilitate a manufacturing process and reduce crosstalk to an adjacent pixel in addition to obtain the advantages of the first to seventh embodiments.

Ninth Embodiment

An imaging system according to a ninth embodiment of the present invention will be described with reference toFIG. 16. Components similar to those of the imaging devices according to the first to eighth embodiments are labeled with the same references, and the description thereof will be omitted or simplified.FIG. 16is a block diagram illustrating a general configuration of the imaging system according to the present embodiment.

The imaging device300described in the above first to eighth embodiments is applicable to various imaging systems. Examples of applicable imaging systems may include a digital still camera, a digital camcorder, a surveillance camera, a copying machine, a fax machine, a mobile phone, an on-vehicle camera, an observation satellite, and the like. In addition, a camera module including an optical system such as a lens and an imaging device is also included in the imaging system.FIG. 16illustrates a block diagram of a digital still camera as an example out of these examples.

The imaging system500illustrated as an example inFIG. 16includes an imaging device501, a lens502that captures an optical image of a subject onto the imaging device501, an aperture504for changing a light amount passing through the lens502, and a barrier506for protecting the lens502. The lens502and the aperture504form an optical system that converges a light onto the imaging device501. The imaging device501is the imaging device300described in any of the first to eighth embodiments. The imaging device501transmits an optical image captured by the lens502on the pixel region204of the sensor substrate200to the readout circuit substrate100via the light receiving unit220and the light emitting unit230of each pixel202. The readout circuit substrate100receives information transmitted from the sensor substrate200by each pixel102arranged in the pixel region104and converts the received information into an image signal.

The imaging system500further includes a signal processing unit508that processes an image signal output from the imaging device501. The signal processing unit508preforms analog-to-digital (AD) conversion that converts an analog signal output by the imaging device501into a digital signal. In addition, the signal processing unit508performs various correction and compression other than the above, if necessary, and outputting image data. An AD converter unit, which is a part of the signal processing unit508, may be provided on a semiconductor substrate on which the imaging device501is provided (the readout circuit substrate100) or may be provided on a semiconductor substrate other than the substrate on which the imaging device501is provided. Further, the imaging device501and the signal processing unit508may be provided on the same semiconductor substrate.

The imaging system500further includes a memory unit510for temporarily storing image data therein and an external interface unit (external I/F unit)512for communicating with an external computer or the like. The imaging system500further includes a storage medium514such as a semiconductor memory for performing storage or readout of image data and a storage medium control interface unit (storage medium control I/F unit)516for performing storage or readout on the storage medium514. Note that the storage medium514may be embedded in the imaging system500or may be removable.

The imaging system500further includes a general control/operation unit518that controls various operations and the entire digital still camera and a timing generation unit520that outputs various timing signals to the imaging device501and the signal processing unit508. Here, the timing signal or the like may be input from the outside, and the imaging system500may include at least the imaging device501and the signal processing unit508that processes an output signal output from the imaging device501.

The imaging device501outputs an image signal to the signal processing unit508. The signal processing unit508performs predetermined signal processing on an image signal output from the imaging device501and outputs image data. The signal processing unit508generates an image by using the image data.

By applying the imaging device300according to the first to eighth embodiments, it is possible to realize an imaging system that may acquire a high definition image of a light of a long wavelength band such as above 1.0 μm.

Modified Embodiments

The present invention is not limited to the embodiments described above, and various modifications are possible.

For example, the material, the configuration, or the like illustrated in the embodiments described above may be appropriately changed as long as the advantage of the present invention is obtained. For example, in the embodiments described above, the pixel region104of the readout circuit substrate100may be configured to be the same as a backside irradiation type CMOS image sensor. Further, in the embodiments described above, an InGaAsSb-based material that may detect a light of a longer wavelength, an AlGaInN-based material that may effectively receive a light of an ultraviolet region, or a II-VI group compound semiconductor material may be applied to the light receiving unit220of the sensor substrate200.

Further, while the readout circuit substrate100and the sensor substrate200are spaced apart by a predetermined spacing and an air layer (air gap) is interposed therebetween in the embodiments described above, a part between the readout circuit substrate100and the sensor substrate200is not necessarily an air layer (air gap). For example, a material transparent to a light emitted from the light emitting unit230, for example, an optical transparent resin may be filled between the readout circuit substrate100and the sensor substrate200. Further, the readout circuit substrate100and the sensor substrate200may be joined so that the surface of the readout circuit substrate100and the surface of the sensor substrate200are in contact with each other.

Further, a light shield member is provided so that no external light enters the light receiving unit220of some of the pixels202provided on the sensor substrate200, and each of those pixels202may be a so-called optical black pixel that monitors a change amount of a dark current or the like due to a change in the surrounding temperature or the like.

According to the present invention, it is possible to provide a high-performance and reliable imaging device and a high-performance and reliable imaging system that include a substrate provided with a light receiving unit and a substrate provided with a readout circuit.