Semiconductor device and imaging device for reading charge

According to an embodiment, a semiconductor device includes a silicon substrate, a photoelectric conversion layer, a termination layer, and an electrode layer. In the silicon substrate, first semiconductor regions and second semiconductor regions are alternately arranged along a first surface on a light incident side of the silicon substrate. The first semiconductor regions are doped with impurities of first concentration and have a conductivity of either one of p-type and n-type. The second semiconductor regions are doped with impurities of a second concentration lower than the first concentration and have a conductivity of the other type. The photoelectric conversion layer is disposed on a first surface side of the silicon substrate. The termination layer is disposed between the silicon substrate and the photoelectric conversion layer, in contact with the first surface, and to terminate dangling bonds of the silicon substrate. The electrode layer is provided on the light incident side.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2015-047489, filed on Mar. 10, 2015; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor device and an imaging device.

BACKGROUND

Semiconductor devices have been known that read charges photoelectrically converted by photoelectric conversion films. For example, a structure of such semiconductor devices has been known in which electrode layers are disposed so as to sandwich a photoelectric conversion film and a silicon substrate including p-type semiconductor regions and n-type semiconductor regions is in an ohmic contact with one of the electrode layers. Moreover, a technique is disclosed in which a photoelectric conversion film is connected to a floating diffusion region via a semiconductor region and a transfer transistor.

Signals read from the semiconductor device include noise due to capacitance of the floating diffusion region in some cases. To eliminate noise, a technique is disclosed that uses a photoelectric conversion film formed of a silicon substrate and having a photoelectric conversion function and a charge accumulation function, and employs a noise elimination technique called correlated double sampling (CDS).

The conventional technique, however, cannot eliminate noise included in the read signals in some cases.

DETAILED DESCRIPTION

According to an embodiment, a semiconductor device includes a silicon substrate, a photoelectric conversion layer, a termination layer, and an electrode layer. In the silicon substrate, first semiconductor regions and second semiconductor regions are alternately and continuously arranged along a first surface on a light incident side of the silicon substrate. The first semiconductor regions are doped with impurities of a first concentration and have a conductivity of either one of a p-type and an n-type. The second semiconductor regions are doped with impurities of a second concentration lower than the first concentration and have a conductivity of the other type. The photoelectric conversion layer is disposed on a first surface side of the silicon substrate. The termination layer is disposed between the silicon substrate and the photoelectric conversion layer, in contact with the first surface of the silicon substrate, and to terminate dangling bonds of the silicon substrate. The electrode layer is provided on the light incident side of the photoelectric conversion layer.

Various embodiments will be described in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1is a schematic diagram illustrating an example of a semiconductor device10according to a first embodiment. The semiconductor device10is applicable to an imaging device100that images an object and obtains the image data of the object, for example.

The semiconductor device10includes a silicon substrate16, a photoelectric conversion layer20, a termination layer22, an electrode layer24, a reading circuit28, a voltage application unit44.

The semiconductor device10has a stacked structure composed of the reading circuit28, the silicon substrate16, the termination layer22, the photoelectric conversion layer20, and the electrode layer24that are stacked in this order. The semiconductor device10in the first embodiment receives light entering from an electrode layer24side toward a silicon substrate16side, and performs photoelectric conversion by the photoelectric conversion layer20. The semiconductor device10reads, by the reading circuit28, a signal according to the charges converted by the photoelectric conversion layer20.

The semiconductor device10according to the first embodiment is thus a stacked-type image sensor in which the photoelectric conversion layer20and the electrode layer24are stacked on a backside-irradiation-type complementary metal oxide semiconductor (CMOS) image sensor. The backside irradiation-type image sensor means the structure in which the reading circuit28is provided on the side opposite a light incident side of the silicon substrate16.

The silicon substrate16includes second semiconductor regions12and first semiconductor regions14that are alternately arranged along a first surface18of the silicon substrate16. The first surface18is the surface of the silicon substrate16on the light incident side of the semiconductor device10. In other words, the first surface18is the surface on a photoelectric conversion layer20side of the silicon substrate16.

The first semiconductor regions14are semiconductor regions doped with impurities of a first concentration. The first semiconductor regions14have a conductivity of either one of a p-type and an n-type. The second semiconductor regions12are semiconductor regions doped with impurities of a second concentration lower than the first concentration. The second semiconductor regions12have a conductivity of the other type.

For example, in the case where charges produced by the photoelectric conversion by the photoelectric conversion layer20are electrons, the second semiconductor regions12are n− (n minus) type semiconductor regions while the first semiconductor regions14are p+ (p plus) type semiconductor regions. In contrast, in the case where charges produced by the photoelectric conversion by the photoelectric conversion layer20are holes, the second semiconductor regions12are the p− type semiconductor regions while the first semiconductor regions14are the n− type semiconductor region.

The first semiconductor regions14are connected to the ground. A relative electric potential difference between the first semiconductor region14and the second semiconductor region12is thus fixed.

In the case where the first semiconductor regions14are the p+ type and the second semiconductor regions12are the n− type, the electric potential of the first semiconductor regions14is lower than that of the second semiconductor regions12. The first semiconductor regions14, thus, function as potential barriers for electrons in the second semiconductor regions12.

Similarly, in the case where the first semiconductor regions14are n+ (n plus) type and the second semiconductor regions12are p− (p minus) type, the electric potential of the first semiconductor regions14is higher than that of the second semiconductor regions12. In this case, the first semiconductor regions14function as potential barriers for holes in the second semiconductor regions12.

Herein, the region including the second semiconductor region12and a part of the first semiconductor regions14adjacent to the second semiconductor region12is defined as a pixel region B as illustrated inFIG. 1.

The first semiconductor regions14function as the potential barriers, as described above. The first semiconductor regions14thus function as pixel separation regions that prevent the electrons from the second semiconductor region12from mixing into the adjacent pixel regions B. The second semiconductor region12functions as a charge accumulation region that accumulates charges converted by the photoelectric conversion layer20.

In the following description, charges are electrons unless otherwise noted. Furthermore, in the following description, the second semiconductor regions12are the n−type while the first semiconductor regions14are the p+ type.

In the semiconductor device10in the first embodiment, charges may be holes and the second semiconductor regions12may be the p− type while the first semiconductor regions14may be the n+ type.

The first semiconductor regions14are the semiconductor regions doped with the impurities of the first concentration, as described above. The second semiconductor regions12are the semiconductor regions doped with the impurities of the second concentration lower than the first concentration, as described above.

The first concentration is higher than the second concentration. Specifically, the first concentration is preferably in a range from 1.0×1014cm−3to 1.0×1017cm−3, and more preferably in a range from 1.3×1014cm−3to 3.6×1016cm−3.

The first semiconductor regions14and the second semiconductor regions12are formed by doping impurities into a silicon layer17(refer toFIG. 2, which is described in detail later). The concentrations of impurities to be doped are adjusted to the respective first and the second concentrations. As a result, the first semiconductor regions14and the second semiconductor regions12are formed.

A first density of the impurities in the first semiconductor region14and a second density of the impurities in the second semiconductor region12preferably satisfy the following expression (1).
Na>Nd×Aa/Ad(1)
where Narepresents the first density of the impurities in the first semiconductor regions14, Ndrepresents the second density of the impurities in the second semiconductor region12, Aarepresents an area of the first semiconductor region14in the pixel region B, and Adrepresents an area of the second semiconductor regions12in the pixel region B. Typically, Aais smaller than Ad(Aa<Ad).

The area of the first semiconductor region14and the area of the second semiconductor regions12in the pixel region B correspond to the area of the first semiconductor region14and the area of the second semiconductor regions12in a cross-section in parallel with the first surface18in the pixel region B of the silicon substrate16, respectively. The direction in parallel with the first surface18is the direction perpendicular to the stacking direction of the silicon substrate16, the termination layer22, the photoelectric conversion layer20, and the electrode layer24in the semiconductor device10.

As a result of the relation between the first density of the impurities in the first semiconductor region14and the second density of the impurities in the second semiconductor region12satisfying the expression (1), the second semiconductor region12can be completely depleted.

The first density Naof the impurities in the first semiconductor region14is in a range from 1×1017cm−3to 1×1018cm−3, for example. The second density Ndof the impurities in the second semiconductor region12is in a range from 1×1016cm−3to 1×1017cm−3, for example. The values of the first density Naand the second density Ndare not limited to those values in the ranges.

The thicknesses of the second semiconductor region12and the first semiconductor region14are not limited to specific values. The thickness of the second semiconductor region12and the first semiconductor region14is 5 μm, for example.

The reading circuit28is provided on a second surface26side of the silicon substrate16. The second surface26is opposite the first surface18located on the light incident side of the silicon substrate16. The reading circuit28reads charges accumulated in the second semiconductor regions12as a signal. The details of the reading circuit28will be described later.

The following describes the photoelectric conversion layer20. The photoelectric conversion layer20is disposed on the first surface18side of the silicon substrate16.

The photoelectric conversion layer20converts light entering the photoelectric conversion layer20through the electrode layer24into charges. The photoelectric conversion layer20includes, as a principal component, an inorganic material such as amorphous silicon that performs photoelectric conversion over the whole visible light range, a compound such as copper indium gallium diselenide (CIGS), or an organic material. The principal component means that the content thereof is equal to or larger than 70%. For the photoelectric conversion layer20, a panchromatic organic photoelectric conversion film may be used.

The material used for the photoelectric conversion layer20is not limited to any specific material. When light in a different wavelength range from that converted by the photoelectric conversion layer20is further photoelectrically converted on the silicon substrate16side of the photoelectric conversion layer20, the photoelectric conversion layer20needs to have a wavelength selectivity. The photoelectric conversion layer20having the wavelength selectivity allows light having a wavelength other than the target wavelength range of the photoelectric conversion of the photoelectric conversion layer20to pass through the photoelectric conversion layer20. In this case, the photoelectric conversion layer20includes quinacridone or subphthalocyanine, for example.

The photoelectric conversion layer20preferably includes an organic material as the principal component.

The use of the photoelectric conversion layer20including an organic material as the principal component makes it possible to further increase a resistivity of the photoelectric conversion layer20than that of the photoelectric conversion layer20including no organic material as the principal component. The higher the resistivity of the photoelectric conversion layer20is, the further charges produced in the photoelectric conversion layer20can be prevented from spreading to the regions corresponding to the other pixel regions B in the photoelectric conversion layer20. In other words, charges from the other pixel regions B can be prevented from mixing into the respective pixel regions B.

The region corresponding to each pixel region B in the photoelectric conversion layer20is the region adjacent to each pixel region B in a thickness direction in the photoelectric conversion layer20with the termination layer22interposed therebetween. The thickness direction is the direction along the thickness of the semiconductor device10and the same direction as the stacking direction of the silicon substrate16, the termination layer22, and the photoelectric conversion layer20.

The use of the photoelectric conversion layer20including an organic material as the principal component can also achieve the following effects. When the photoelectric conversion layer20including an organic material as the principal component is stacked on the silicon substrate16without interposing an electrode layer (lower electrode layer) therebetween, no fine processing is required for forming the lower electrode layer. Furthermore, the pixel region B including the second semiconductor region12and the first semiconductor regions14can be readily formed by adjusting the concentrations of the impurities doped into the silicon layer17.

In the semiconductor device10in the first embodiment, the photoelectric conversion layer20is a continuous film continuously provided along the arrangement direction of the second semiconductor regions12that function as the charge accumulation region. The photoelectric conversion layer20is thus continuously provided over the multiple pixel regions B.

The electrode layer24is provided on the light incident side of the photoelectric conversion layer20. The electrode layer24may be made of a material that transmits light having a wavelength range that is the detection target by the semiconductor device10and that has conductivity. The electrode layer24is made of a material such as indium tin oxide (ITO), graphene, or zinc oxide (ZnO).

The thickness of the electrode layer24is not limited to any specific thickness. The thickness of the electrode layer24is 35 nm, for example.

The termination layer22is disposed between the silicon substrate16and the photoelectric conversion layer20. The termination layer22is disposed in contact with at least the first surface18of the silicon substrate16. The termination layer22may be disposed in such a manner that another layer is interposed between the termination layer22and the photoelectric conversion layer20. In other words, the termination layer22may be disposed without being in contact with the photoelectric conversion layer20.

The termination layer22is preferably disposed in contact with both of the silicon substrate16and the photoelectric conversion layer20. Specifically, the termination layer22is preferably disposed in contact with both of the first surface18of the silicon substrate16and a third surface19of the photoelectric conversion layer20. The third surface19is a surface of the photoelectric conversion layer20on a side adjacent to the silicon substrate16.

The termination layer22terminates surface dangling bonds of the silicon substrate16.

Here, the photoelectric conversion layer20is assumed to be stacked on un-terminated dangling bonds on the surface of the silicon substrate16. When the photoelectric conversion layer20is stacked on the un-terminated dangling bonds on the surface of the silicon substrate16, an interface level is formed in an interface between the silicon substrate16and the photoelectric conversion layer20. The interface level acts as a trap of charges converted by the photoelectric conversion layer20.

The interface level acting as a trap causes noise and an afterimage to occur in a signal read by the reading circuit28. The interface level acting as a trap causes band bending to occur in the interface between the silicon substrate16and the photoelectric conversion layer20, thereby hindering complete transfer of charges from the photoelectric conversion layer20to the silicon substrate16.

To address such situations, the semiconductor device10in the embodiment includes the termination layer22disposed between the first surface18and the photoelectric conversion layer20. The termination layer22terminates the dangling bonds on the surface of the silicon substrate16.

The termination layer22may be a layer having a function to terminate the surface dangling bonds of the silicon substrate16. The termination layer22is a silicon dioxide film, for example.

The termination layer22may be a region where all of the dangling bonds on the surface of the silicon layer17are terminated by hydrogen, for example.FIG. 2is an explanatory view of the termination layer22.

The silicon layer17illustrated inFIG. 2is prepared. The silicon layer17is an un-terminated layer in the silicon substrate16. The silicon layer17includes the first semiconductor regions14and the second semiconductor regions12that are alternately and continuously arranged on the surface thereof. The dangling bonds on the surface of the silicon layer17are terminated by hydrogen by treating the surface with hydrofluoric acid, for example.

In this case, the termination layer22is a region where the surface dangling bonds are terminated with hydrogen in the silicon layer17. In this case, the termination layer22is a Si—H layer where the dangling bonds on the surface of the silicon layer17are terminated with hydrogen atoms. In this case, the silicon substrate16is the region that continues on the second surface26side of the termination layer22in the silicon layer17.

The termination layer22may have a thickness that allows charges produced in the photoelectric conversion layer20to pass through the termination layer22to the silicon substrate16. For example, when the termination layer22is a silicon dioxide film, the thickness of the termination layer22is preferably equal to or smaller than 2 nm. The thickness of the termination layer22may be 1.5 nm, for example.

In the case where the termination layer22is a silicon dioxide film, a direct tunneling phenomenon occurs when an electric field intensity in the film is 1 to 2 MV/cm. The direct tunneling phenomenon means that substantially 100% of charges that drift from the photoelectric conversion layer20toward the silicon substrate16pass through the termination layer22to the silicon substrate16. From this point of view, the thickness of the termination layer22is preferably equal to or smaller than 2 nm when the termination layer22is a silicon dioxide film.

Referring back toFIG. 1, the following describes a flow of charges in the semiconductor device10in the embodiment.

When light traveling from the electrode layer24side to the photoelectric conversion layer20enters the semiconductor device10thus structured, the photoelectric conversion layer20converts incident light into charges.

The charges produced by the photoelectric conversion layer20are drifted by an electric field formed in the thickness direction of the semiconductor device10in the photoelectric conversion layer20toward the silicon substrate16, and reach the termination layer22. The thickness direction of the semiconductor device10is the same direction as the stacking direction of the respective layers included in the semiconductor device10.

When the photoelectric conversion layer20includes an organic material as the principal component, charges produced by the photoelectric conversion layer20are prevented from moving in the direction intersecting with the stacking direction and drifting toward the other pixel regions B, as described above.

When the termination layer22is not provided, the produced charges are trapped by the interface level formed in the interface between the silicon substrate16and the photoelectric conversion layer20, thereby causing noise, as described above. The semiconductor device10in the embodiment, however, includes the termination layer22provided between the silicon substrate16and the photoelectric conversion layer20.

As a result, charges that drift in the photoelectric conversion layer20toward the silicon substrate16and that reach the third surface19of the photoelectric conversion layer20completely (substantially 100%) pass through the termination layer22to the silicon substrate16.

The first semiconductor region14in the silicon substrate16functions as the potential barrier for charges reaching the second semiconductor region12, as described above. As a result, an electric field that causes charges to drift from the first semiconductor region14toward the second semiconductor region12is formed between the second semiconductor region12and the first semiconductor region14. The charges having reached the silicon substrate16from the photoelectric conversion layer20through the termination layer22are collected in the second semiconductor region12for each pixel region B by the electric field directing from the first semiconductor region14toward the second semiconductor region12.

The second semiconductor region12has been depleted. The charges produced by the photoelectric conversion layer20are thus accumulated in the second semiconductor region12without being mixed with charges already accumulated in the silicon substrate16. The charges accumulated in the second semiconductor region12are read by the reading circuit28as a signal.

When the first semiconductor region14is not completely depleted, a region near the central region in the direction perpendicular to the thickness direction in the first semiconductor region14becomes a flat band where no electric field is formed. As a result, charges that reach this region of the silicon substrate16from the photoelectric conversion layer20through the termination layer22are instantaneously recombined with the charges (holes or electrons) that are majority carriers in the first semiconductor region14, thereby drifting to the second semiconductor region12side. Consequently, charges are prevented from remaining in the first semiconductor region14for a long time, thereby also preventing the occurrence of an afterimage.

When the semiconductor device10converts light into charges, the voltage application unit44applies a voltage to the electrode layer24.

The voltage applied by the voltage application unit44to the electrode layer24may have a value equal to or larger than a voltage value necessary to allow charges to pass through the termination layer22by direct tunneling.

The specific value of the voltage applied by the voltage application unit44to the electrode layer24may be appropriately adjusted in accordance with the structure of the semiconductor device10so as to satisfy the condition described above.

For example, the size of the pixel region B is assumed to be 1 μm by 1 μm. The size of the pixel region B is the size of a surface in parallel with the first surface18, which is a two-dimensional plane, in the pixel region B. The thickness of the silicon substrate16is assumed to be 5 μm. The width of the first semiconductor region14in the pixel region B is assumed to be 125 nm. The width of the first semiconductor region14in the pixel region B corresponds to half of the distance between the two adjacent second semiconductor regions12. The size of the second semiconductor region12in the pixel region B is assumed to be 750 nm by 750 nm. The number of saturation electrons in the first semiconductor region14is assumed to be 100,000. The number of atoms of the impurities in the second semiconductor region12is equal to the number of saturation electrons.

In this case, the second density Ndof the impurities in the second semiconductor region12is obtained by the following expression (2). The lower limit value (Namin) of the first density Na of the impurities in the first semiconductor region14is obtained by the following expression (3).
Nd(cm−3)=100,000/(750 nm×750 nm×5 μm)  (2)
Namin=100,000/[(1 μm×1 μm−750 nm×750 nm)]×5 μm  (3)

When the first density of the impurities in the first semiconductor region14is equal to the value of Naminrepresented by the expression (3), then the flat band area in the first semiconductor region14disappears. When the relation represented by the expression (3) is satisfied, the first semiconductor region14is also completely depleted in the same manner as the second semiconductor region12.

When both of the second semiconductor region12and the first semiconductor region14are completely depleted, all of the charges transferred from the photoelectric conversion layer20to the silicon substrate16through the termination layer22drift to the second semiconductor region12in any of the pixel regions B. Thus, all of the charges transferred from the photoelectric conversion layer20to the silicon substrate16are read by the reading circuit28. When the expressions (2) and (3) are satisfied, an effective aperture ratio of the semiconductor device10used as an image sensor becomes the highest value.

The electric potential in the second semiconductor region12is represented by the following expression (A) when the first density Naof the impurities in the first semiconductor region14is Namin. The expression (A) is obtained by linearly approximating an electric potential profile between the second semiconductor region12and the first semiconductor region14(refer to A-A′ region inFIG. 1) and solving a Poisson equation.

Vbi=qNa⁢xp22⁢ɛSi⁢ɛ0+qNd⁢xp22⁢ɛSi⁢ɛ0(A)
where Vbirepresents the electric potential in the second semiconductor region12, εsirepresents the permittivity of silicon, ε0represents the permittivity of vacuum, Xprepresents the distance (on the first semiconductor region14side) from the junction surface of the second semiconductor region12and the first semiconductor region14, Xnrepresents the distance (on the second semiconductor region12side) from the junction surface of the second semiconductor region12and the first semiconductor region14, q represents the elementary electric charge, Nais the first density of the impurities in the first semiconductor region14, and Ndis the second density of the impurities in the second semiconductor region12.

The electric potential of the central region in the direction perpendicular to the stacking direction in the second semiconductor region12can be estimated as 4.53 V from the expression (A). In this case, a relation between the electric potential of the applied voltage to the electrode layer24and the electric field intensity in the termination layer22is illustrated inFIG. 3.

FIG. 3is a schematic diagram illustrating the relation between the electric potential of the applied voltage to the electrode layer24and the electric field intensity in the termination layer22.

In the example illustrated inFIG. 3, an organic photoelectric conversion film having a thickness of 100 nm is used for the photoelectric conversion layer20. A silicon dioxide film having a thickness of 1.5 nm is used for the termination layer22. The calculation results of the electric field intensity in the termination layer22at an initial state (refer to line50) and at accumulation of a saturation charge amount (refer to line52) are illustrated inFIG. 3. At the initial state, an amount of accumulated charges in the second semiconductor region12is “zero”. At the accumulation of a saturation charge amount, the difference in electric potential between the second semiconductor region12and the first semiconductor region14is 0 V.

As described above, in the case where the termination layer22is a silicon dioxide film, the direct tunneling phenomenon occurs when the electric field intensity in the film is 1 to 2 MV/cm. From the results illustrated inFIG. 3, when the first density of the impurities of the first semiconductor region14is Namin, the second density of the impurities of the second semiconductor region12satisfies the expression (2), the organic photoelectric conversion film having a thickness of 100 nm is used for the photoelectric conversion layer20, and the silicon dioxide film having a thickness of 1.5 nm is used for the termination layer22, then the direct tunneling phenomenon occurs by applying a negative bias equal to or smaller than −4 V to the electrode layer24.

Thus, in this case, the voltage application unit44may apply a negative bias equal to or smaller than −4 V to the electrode layer24.

The following describes the reading circuit28in detail.

FIG. 4is a schematic diagram illustrating the structure of the reading circuit28of the semiconductor device10. The reading circuit28reads the charges accumulated in the second semiconductor region12as a signal.

The reading circuit28includes a transfer transistor30, a third semiconductor region32, and a wiring layer34.

The transfer transistor30, which is connected to the second semiconductor region12, transfers the charges accumulated in the second semiconductor region12to the third semiconductor region32.

The transfer transistor30may be a lateral transistor or a vertical transistor. The transfer transistor30is, however, preferably the vertical transistor. The use of the vertical transistor for the transfer transistor30makes it possible to form the pixel regions B in the semiconductor device10into finer regions. The application of the semiconductor device10thus structured to the imaging device100can achieve the imaging device100that provides high image quality.

The third semiconductor region32, which is connected to the transfer transistor30, converts the charges transferred from the transfer transistor30into a voltage. The third semiconductor region32, which has a tiny capacitance, is called a floating diffusion. A conversion gain (gain for converting the charges into a voltage) of the third semiconductor region32is determined by the capacitance of the third semiconductor region32. The higher the capacitance of the third semiconductor region32is, the higher the conversion gain is. The third semiconductor region32is connected to the wiring layer34.

The wiring layer34outputs, as a signal, the voltage converted by the third semiconductor region32. In the embodiment, the wiring layer34includes a reset transistor36, an amplifier transistor38, a selector transistor40, and a correlated double sampling (CDS)42. In the semiconductor device10in the embodiment, the reading circuit28includes four transistors (the transfer transistor30, the reset transistor36, the amplifier transistor38, and the selector transistor40).

The third semiconductor region32is connected to a gate of the amplifier transistor38. The voltage converted by the third semiconductor region32is output from a source of the amplifier transistor38to the CDS42through the selector transistor40.

The third semiconductor region32is connected to the source of the reset transistor36. To a drain of the reset transistor36, a power supply potential (Vrst), which is a reset level of the third semiconductor region32, is connected.

The CDS42is a circuit that performs correlated double sampling. The CDS42eliminates noise by correlated double sampling from the signal that is output from the third semiconductor region32and transmitted through the amplifier transistor38and the selector transistor40. The CDS42outputs the signal after the noise elimination as a signal read from the second semiconductor region12.

FIG. 5is an exemplary timing chart illustrating reading of a signal by the reading circuit28. The control of the reading circuit28is performed by a controller, which is not illustrated.

InFIG. 5, line60illustrates on and off states of the reset transistor36. Line62illustrates on and off states of the transfer transistor30. Line64illustrates on and off states of the third semiconductor region32. Line66illustrates the electric potential of the second semiconductor region12that accumulates charges. Line68illustrates on and off states of the amplifier transistor38.

At timing t0, the transfer transistor30is turned on as denoted by62A and the reset transistor36is turned on as denoted by60A. As a result, reset operation is performed on the second semiconductor region12and the third semiconductor region32. The reset operation causes the electric potential of the second semiconductor region12to be in the initial state. The reset operation is not mandatory. The reason is that charges are completely transferred from the second semiconductor region12to the third semiconductor region32, in the embodiment.

At timing t1, the transfer transistor30is turned off as denoted by62B. Likewise, the reset transistor36is turned off as denoted by60B. As a result of the tuning off of the transfer transistor30as denoted by62B, accumulation of charges in the second semiconductor region12starts (refer to an accumulation period C inFIG. 5). In the accumulation period, charges produced by the photoelectric conversion layer20reach the silicon substrate16through the termination layer22and are accumulated in the second semiconductor region12. The electric potential of the second semiconductor region12thus reduces with an increase in accumulation of charges (electrons) (refer to line66A inFIG. 5).

When this accumulation period ends, at timing t2, the reset transistor36is turned on as denoted by60C while the transfer transistor30remains to be turned off as denoted by62B. As a result, only the third semiconductor region32is reset. After the reset of the third semiconductor region32(refer to timing t3), the amplifier transistor38is turned on as denoted by68B from the turned off state denoted by68A. As a result, the amplifier transistor38reads the reset level of the third semiconductor region32. After the reset level is read, the amplifier transistor38is turned off as denoted by68C from the turned on state denoted by68B. The reset level read by the amplifier transistor38is sampled and held by the CDS42.

At timing t4, the transfer transistor30is turned on as denoted by62C. As a result, the charges accumulated in the second semiconductor region12are completely transferred to the third semiconductor region32. Thereafter, at timing t5, the amplifier transistor38is turned on as denoted by68D from the turned off state as denoted by68C. As a result, the CDS42reads a signal level. After the signal level is read, the amplifier transistor38is turned off.

The CDS42performs CDS processing on the read signal level using the reset level that is sampled and held, and reads the signal.

As described above, the semiconductor device10in the embodiment includes the silicon substrate16, the photoelectric conversion layer20, the termination layer22, and the electrode layer24. The silicon substrate16includes the second semiconductor regions12and the first semiconductor regions14that are alternately and continuously arranged along the first surface18on the light incident side. The first semiconductor regions14are doped with the impurities of the first concentration and have the conductivity of either one of the p-type and the n-type. The second semiconductor regions12are doped with the impurities of the second concentration lower than the first concentration and have the conductivity of the other type. The photoelectric conversion layer20is disposed on the first surface18side of the silicon substrate16. The termination layer22is disposed between the silicon substrate16and the photoelectric conversion layer20in contact with the first surface18of the silicon substrate16, and terminates the dangling bonds of the silicon substrate16. The electrode layer24is provided on the light incident side of the photoelectric conversion layer20.

The semiconductor device10in the embodiment includes the termination layer22that is disposed between the silicon substrate16and the photoelectric conversion layer20in contact with the first surface18of the silicon substrate16, as described above. The termination layer22terminates the dangling bonds on the surface of the silicon substrate16.

As a result, the charges that are photoelectrically converted by the photoelectric conversion layer20drift to the silicon substrate16without being trapped by the interface level in the interface between the silicon substrate16and the photoelectric conversion layer20, and are accumulated in the second semiconductor region12. The semiconductor device10in the embodiment reads the charges accumulated in the second semiconductor region12as a signal.

The semiconductor device10in the embodiment can thus reduce noise included in the read signal.

The semiconductor device10applied to the imaging device100can also obtain the same effect.

In the semiconductor device10in the embodiment, the photoelectric conversion layer20and the silicon substrate16are stacked with the termination layer22interposed therebetween without providing an electrode layer (lower electrode) between the photoelectric conversion layer20and the silicon substrate16.

With the semiconductor device10in the embodiment, the electrode layer (lower electrode) between the photoelectric conversion layer20and the silicon substrate16does not require to be finely processed so as to be fitted with the pixel region B. That is, the semiconductor device10in the embodiment does not require fine processing on the lower electrode for pixel separation. The semiconductor device10in the embodiment can readily form the pixel regions B by forming the second semiconductor regions12and the first semiconductor region14as a result of doping impurities into the silicon substrate16.

The pixel regions B of the semiconductor device10in the embodiment can also be formed without performing fine processing on the lower electrode layer for pixel separation, while having the effect described above.

Second Embodiment

The following describes the imaging device100according to a second embodiment. The imaging device100in the second embodiment includes the semiconductor device10in the first embodiment provided with a color filter.

FIG. 6is a schematic diagram illustrating an example of an imaging device100A in the second embodiment. The components having the same functions as the semiconductor device10in the first embodiment are labeled with the same numerals, and detailed descriptions thereof are thus omitted.

The imaging device100A includes the reading circuit28, the silicon substrate16, the termination layer22, the photoelectric conversion layer20, the electrode layer24, a color filter76, and the voltage application unit44.

The second semiconductor region12of the silicon substrate16is connected to the reading circuit28through a source terminal70. Specifically, the second semiconductor region12is connected to the transfer transistor30of the reading circuit28. On the surface opposite the silicon substrate16of the reading circuit28, an insulation layer74is stacked in such a manner that the insulation layer74includes wiring layers72provided on the surface.

The color filter76is disposed at the light incident side of the electrode layer24. The color filter76includes, for each pixel region B, a color filter76R that absorbs light having a red wavelength range, a color filter76B that absorbs light having a blue wavelength range, and a color filter76G that absorbs light having a green wavelength range. The color filters76R,76B, and76G are preferably arranged in a Bayer arrangement.

The thickness of the color filter76is not limited to any specific thickness. The thickness of the color filter76is 100 nm, for example.

As illustrated inFIG. 6, the imaging device100A in the embodiment includes the color filter76above the electrode layer24. The color filter76includes, for each region corresponding to each pixel region B, the color filter76R that absorbs light having the red wavelength range, the color filter76B that absorbs light having the blue wavelength range, and the color filter76G that absorbs light having the green wavelength range.

Thus, the imaging device100A in the embodiment can read, for each pixel region B, signals according to charges corresponding to respective light components R (light in the red wavelength range), G (light in the green wavelength range), and B (light in the blue wavelength range).

As described above, the imaging device100A in the embodiment can achieve the same effect as the first embodiment because the imaging device100A includes the termination layer22while the color filter76is provided.

Third Embodiment

The following describes the imaging device100according to a third embodiment. The imaging device100in the third embodiment includes the semiconductor device10in the first embodiment provided with a color filter different from that in the second embodiment.

FIG. 7is a schematic diagram illustrating an example of an imaging device100B in the third embodiment. The components having the same functions as the semiconductor device10in the first embodiment are labeled with the same numerals, and detailed descriptions thereof are thus omitted.

The imaging device100B includes the reading circuit28, a silicon substrate162, the termination layer22, a photoelectric conversion layer20B, the electrode layer24, a color filter76Y, and the voltage application unit44(not illustrated inFIG. 7).

The photoelectric conversion layer20B converts incident light into charges in the same manner as the photoelectric conversion layer20. In the embodiment, the photoelectric conversion layer20B performs photoelectric conversion on light in the blue wavelength range and on light in the green wavelength range. Light in the red wavelength range passes through the photoelectric conversion layer20B.

The color filter76Y is a yellow color filter that absorbs light in the blue wavelength range. The color filter76Y is provided to the region corresponding to a pixel region B1above the electrode layer24. No color filter76Y is provided to the region corresponding to a pixel region B2, which is the pixel region B adjacent to the pixel region B1.

The silicon substrate162includes the second semiconductor regions12and the first semiconductor regions14that are alternately and continuously arranged along the first surface18in the same manner as the silicon substrate16. The second semiconductor region12is connected to the reading circuit28through the source terminal70.

The size of each pixel region B is assumed to be 1 μm by 1 μm. The size of the second semiconductor region12in each pixel region B is assumed to be 750 nm by 750 nm, and the thickness of the second semiconductor region12is assumed to be 300 nm. The width of the first semiconductor region14in each pixel region B is assumed to be 125 nm. In this case, the second concentration Ndof the second semiconductor region12is estimated as 1×1016cm−3to 1×1017cm−3, and the number of saturation electrons is estimated as 10,000 to 20,000.

The silicon substrate162further includes photoelectric conversion sections78B. Each of the photoelectric conversion sections78B is disposed in the first semiconductor region14on the reading circuit28side of the second semiconductor region12. The photoelectric conversion section78B performs photoelectric conversion on light in the red wavelength region. The photoelectric conversion section78B is a silicon photo diode (SiPD) that performs photoelectric conversion on light in the red wavelength region, for example. The photoelectric conversion sections78B are connected to the reading circuit28. On the surface opposite the silicon substrate162of the reading circuit28, the insulation layer74is stacked in such a manner that the insulation layer74includes the wiring layers72provided on the surface.

The n-type region of the photoelectric conversion section78B is completely depleted by a pn junction between the n-type region of the photoelectric conversion section78B and the first semiconductor region14, which is the p+ region surrounding the photoelectric conversion section78B. The thickness of the silicon substrate162from the first surface18to the photoelectric conversion section78B is 4 μm, for example. Substantially 100% of light in the red wavelength range entering the silicon substrate162having such a thickness is photoelectrically converted by the photoelectric conversion section78B.

The second semiconductor region12is preferably formed in an extremely thin region below the surface of the silicon substrate162so as to have a thin thickness. Specifically, the thickness of the second semiconductor region12is preferably equal to or smaller than 300 nm. The second semiconductor region12having a thickness corresponding to an extremely thin region below the surface of the silicon substrate162can prevent part of light in the red wavelength range after passing through the photoelectric conversion layer20B from being photoelectrically converted by the pn junction between the second semiconductor region12and the first semiconductor region14and causing a mixed color signal.

When light enters the imaging device100B thus structured, the color filter76Y absorbs light in the blue wavelength range from light entering the region corresponding to the pixel region B1on the electrode layer24. The region corresponding to the pixel region B1in the photoelectric conversion layer20B photoelectrically converts light in the green wavelength range into charges. The produced charges corresponding to light in the green wavelength range reach the second semiconductor region12in the pixel region B1through the termination layer22, and are accumulated in the second semiconductor region12. The photoelectric conversion section78B disposed on the reading circuit28side of the second semiconductor region12in the pixel region B1accumulates light in the red wavelength range.

As a result, the signals according to the respective charges corresponding to light in the green wavelength range and light in the red wavelength range can be detected in the pixel region B1.

Light entering the region corresponding to the pixel region B2on the electrode layer24reaches the photoelectric conversion layer20B without passing through the color filter76Y. The region corresponding to the pixel region B2in the photoelectric conversion layer20B photoelectrically converts light in the green wavelength range and light in the blue wavelength range into charges. The produced charges corresponding to light in the green wavelength range and light in the blue wavelength range reach the second semiconductor region12in the pixel region B2through the termination layer22, and are accumulated in the second semiconductor region12. The second semiconductor region12in the pixel region B2accumulates the sum of the signal according to the charges corresponding to light in the green wavelength range and the signal according to the charges corresponding to light in the blue wavelength range.

The photoelectric conversion section78B disposed on the reading circuit28side of the second semiconductor region12in the pixel region B2accumulates light in the red wavelength range.

The reading circuit28, which reads the charges accumulated in the second semiconductor region12and the photoelectric conversion section78B in the pixel region B2, calculates a signal according to the charges corresponding to light in the blue wavelength range by subtracting the signal corresponding to light in the green wavelength range obtained by the adjacent pixel region B1from the signals (sum of the signals corresponding to light in the blue and green wavelength ranges) accumulated in the second semiconductor region12in the pixel region B2.

As a result, the signals according to the charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range can be detected in the pixel region B2.

The imaging device100B thus handles, as one pixel, the region including the pixel region B1to which the color filter76Y is provided and the pixel region B2that is adjacent to the pixel region B1and to which no color filter76Y is provided. As a result, the imaging device100B can detect, for each pixel, the signals according to the respective charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range.

Instead of the yellow color filter76Y that absorbs light in the blue wavelength range, the magenta color filter76that absorbs light in the green wavelength range may be disposed above the pixel region B1. Light in the green wavelength range is used as the principal component of a luminance signal. Light in the green wavelength range is thus preferably detectable by each of all of the pixel regions B. From this point of view, the color filter76Y is preferably used for the color filter76disposed above the pixel region B1.

The longer the wavelength is, the further reduced an absorption coefficient of silicon is. Taking into consideration the mixing of signals corresponding to different colors in the second semiconductor region12, the wavelength of light photoelectrically converted by the photoelectric conversion section78B (the wavelength of light passing through the second semiconductor region12) is preferably a longer wavelength, i.e., light in the red wavelength range is preferable.

As described above, the imaging device100B in the embodiment can achieve the same effect as the first embodiment because the imaging device100B includes the termination layer22while the color filter76Y is provided.

Fourth Embodiment

The following describes the imaging device100according to a fourth embodiment. The imaging device100in the fourth embodiment includes the semiconductor device10in the first embodiment provided with a color filter different from that in the second embodiment.

FIG. 8is a schematic diagram illustrating an example of an imaging device100C in the fourth embodiment. The components having the same functions as the semiconductor device10in the first embodiment are labeled with the same numerals, and detailed descriptions thereof are thus omitted.

The imaging device100C includes the reading circuit28, a silicon substrate164, the termination layer22, a photoelectric conversion layer20C, the electrode layer24, a color filter76C, and the voltage application unit44.

The photoelectric conversion layer20C converts incident light into charges in the same manner as the photoelectric conversion layer20. In the embodiment, the photoelectric conversion layer20C performs photoelectric conversion on light in the red wavelength range and on light in the green wavelength range. Light in the blue wavelength range passes through the photoelectric conversion layer20C.

The color filter76C is a cyan color filter that absorbs light in the red wavelength range. The color filter76C is provided to the region corresponding to a pixel region B3above the electrode layer24. No color filter76C is provided to the region corresponding to a pixel region B4, which is the pixel region B adjacent to the pixel region B3.

The silicon substrate164includes the second semiconductor regions12and the first semiconductor regions14that are alternately and continuously arranged along the first surface18in the same manner as the silicon substrate16.

The silicon substrate164further includes photoelectric conversion sections78C. Each of the photoelectric conversion sections78C is disposed in the first semiconductor region14on the reading circuit28side of the second semiconductor region12. The photoelectric conversion section78C performs photoelectric conversion on light in the blue wavelength region. The photoelectric conversion section78C is a SiPD that performs photoelectric conversion on light in the blue wavelength region, for example. The photoelectric conversion sections78C are connected to the reading circuit28. On the surface opposite the silicon substrate164of the reading circuit28, the insulation layer74is stacked in such a manner that the insulation layer74includes the wiring layers72provided on the surface.

The n-type region of the photoelectric conversion section78C is completely depleted by a pn junction between the n-type region of the photoelectric conversion section78C and the first semiconductor region14, which is the p+ region surrounding the photoelectric conversion section78C. The thickness of the silicon substrate164from the first surface18to the photoelectric conversion section78C is 4 μm, for example. Substantially 100% of light in the blue wavelength range entering the silicon substrate164having such thickness is photoelectrically converted by the photoelectric conversion section78C.

When light enters the imaging device100C thus structured, the color filter76C absorbs light in the red wavelength range from light entering the region corresponding to the pixel region B3on the electrode layer24. The region corresponding to the pixel region B3in the photoelectric conversion layer20C photoelectrically converts light in the green wavelength range into charges. The produced charges corresponding to light in the green wavelength range reach the second semiconductor region12in the pixel region B3through the termination layer22, and are accumulated in the second semiconductor region12. The photoelectric conversion section78C disposed on the reading circuit28side of the second semiconductor region12in the pixel region B3accumulates light in the blue wavelength range.

As a result, the signals according to the respective charges corresponding to light in the green wavelength range and light in the blue wavelength range can be detected in the pixel region B3.

Light entering the region corresponding to the pixel region B4on the electrode layer24reaches the photoelectric conversion layer20C without passing through the color filter76C. The region corresponding to the pixel region B4in the photoelectric conversion layer20C photoelectrically converts light in the green wavelength range and light in the red wavelength range into charges. The produced charges corresponding to light in the green wavelength range and light in the red wavelength range reach the second semiconductor region12in the pixel region B4through the termination layer22, and are accumulated in the second semiconductor region12. The second semiconductor region12in the pixel region B4accumulates the sum of the signal according to the charges corresponding to light in the green wavelength range and the signal according to the charges corresponding to light in the red wavelength range.

The photoelectric conversion section78C disposed on the reading circuit28side of the second semiconductor region12in the pixel region B4accumulates light in the blue wavelength range.

The reading circuit28, which reads the respective charges accumulated in the second semiconductor region12and the photoelectric conversion section78C in the pixel region B4, calculates a signal according to the charges corresponding to light in the red wavelength range by subtracting the signal corresponding to light in the green wavelength range obtained by the adjacent pixel region B3from the signals (the sum of the signals corresponding to light in the red and green wavelength ranges) accumulated in the second semiconductor region12in the pixel region B3.

As a result, the signals according to the respective charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range can be detected in the pixel region B4.

The imaging device100C thus handles, as one pixel, the region including the pixel region B3to which the color filter76C is provided and the pixel region B4that is adjacent to the pixel region B3and to which no color filter76C is provided. As a result, the imaging device100C can detect, for each pixel, the signals according the respective charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range.

As described above, the imaging device100C in the embodiment can achieve the same effect as the first embodiment because the imaging device100C includes the termination layer22while the color filter76C is provided.

Fifth Embodiment

The following describes the imaging device100according to a fifth embodiment. The imaging device100in the fifth embodiment includes the semiconductor device10in the first embodiment provided with a color filter different from that in the second embodiment.

FIG. 9is a schematic diagram illustrating an example of an imaging device100D in the fifth embodiment. The components having the same functions as the semiconductor device10in the first embodiment are labeled with the same numerals, and detailed descriptions thereof are thus omitted.

The imaging device100D includes the reading circuit28, a silicon substrate166, the termination layer22, a photoelectric conversion layer20D, the electrode layer24, the color filter76C, and the voltage application unit44(omitted to be illustrated inFIG. 9). The color filter76C is the same as that in the fourth embodiment.

The photoelectric conversion layer20D converts incident light into charges in the same manner as the photoelectric conversion layer20. In the embodiment, the photoelectric conversion layer20D performs photoelectric conversion on light in the red wavelength range and on light in the blue wavelength range. Light in the green wavelength range passes through the photoelectric conversion layer20D.

The color filter76C is the same as that in the fourth embodiment. The color filter76C is provided to the region corresponding to a pixel region B5above the electrode layer24. No color filter76C is provided to the region corresponding to a pixel region B6, which is the pixel region B adjacent to the pixel region B5.

The silicon substrate166includes the second semiconductor regions12and the first semiconductor regions14that are alternately and continuously arranged along the first surface18in the same manner as the silicon substrate16.

The silicon substrate166further includes photoelectric conversion sections78D. Each of the photoelectric conversion sections78D is disposed in the first semiconductor region14on the reading circuit28side of the second semiconductor region12. The photoelectric conversion section78D performs photoelectric conversion on light in the green wavelength region. The photoelectric conversion section78D is a SiPD that performs photoelectric conversion on light in the green wavelength region, for example. The photoelectric conversion sections78D are connected to the reading circuit28. On the surface opposite the silicon substrate166of the reading circuit28, the insulation layer74is stacked in such a manner that the insulation layer74includes the wiring layers72provided on the surface.

The n-type region of the photoelectric conversion section78D is completely depleted by a pn junction between the n-type region of the photoelectric conversion section78D and the first semiconductor region14, which is the p+ region surrounding the photoelectric conversion section78D. The thickness of the silicon substrate166from the first surface18to the photoelectric conversion section78D is 4 μm, for example. Substantially 100% of light in the green wavelength range entering the silicon substrate166having such thickness is photoelectrically converted by the photoelectric conversion section78D.

When light enters the imaging device100D thus structured, the color filter76C absorbs light in the red wavelength range from light entering the region corresponding to the pixel region B5on the electrode layer24. The region corresponding to the pixel region B5in the photoelectric conversion layer20D photoelectrically converts light in the blue wavelength range into charges. The produced charges corresponding to light in the blue wavelength range reach the second semiconductor region12in the pixel region B5through the termination layer22, and are accumulated in the second semiconductor region12. The photoelectric conversion section78D disposed on the reading circuit28side of the second semiconductor region12in the pixel region B5accumulates light in the green wavelength range.

As a result, the signals according the respective charges corresponding to light in the green wavelength range and light in the blue wavelength range can be detected in the pixel region B5.

Light entering the region corresponding to a pixel region B6on the electrode layer24reaches the photoelectric conversion layer20D without passing through the color filter76C. The region corresponding to the pixel region B6in the photoelectric conversion layer20D photoelectrically converts light in the blue wavelength range and light in the red wavelength range into charges. The produced charges corresponding to light in the blue wavelength range and light in the red wavelength range reach the second semiconductor region12in the pixel region B6through the termination layer22, and are accumulated in the second semiconductor region12. The second semiconductor region12in the pixel region B6accumulates the sum of the signal according to the charges corresponding to light in the blue wavelength range and the signal according to the charges corresponding to light in the red wavelength range.

The photoelectric conversion section78D disposed on the reading circuit28side of the second semiconductor region12in the pixel region B6accumulates light in the green wavelength range.

The reading circuit28, which reads the respective charges accumulated in the second semiconductor region12and the photoelectric conversion section78D in the pixel region B6, calculates a signal according to the charges corresponding to light in the red wavelength range by subtracting the signal corresponding to light in the blue wavelength range obtained by the adjacent pixel region B5from the signals (the sum of the signals corresponding to light in the blue and red wavelength ranges) accumulated in the second semiconductor region12in the pixel region B6.

As a result, the signals according to the respective charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range can be detected in the pixel region B6.

The imaging device100D thus handles, as one pixel, the region including the pixel region B5to which the color filter76C is provided and the pixel region B6that is adjacent to the pixel region B5and to which no color filter76C is provided. As a result, the imaging device100D can detect, for each pixel, the signals according the respective charges corresponding to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range.

As described above, the imaging device100D in the embodiment can achieve the same effect as the first embodiment because the imaging device100D includes the termination layer22while the color filter76C is provided.

Sixth Embodiment

The following describes the imaging device100according to a sixth embodiment. The imaging device100in the six embodiment includes the semiconductor device10in the first embodiment provided with a color variable layer and an optical system.

FIG. 10is a schematic diagram illustrating an example of an imaging device100E in the sixth embodiment. The components having the same functions as the semiconductor device10in the first embodiment are labeled with the same numerals, and detailed descriptions thereof are thus omitted.

The imaging device100E includes the reading circuit28, the silicon substrate16, the termination layer22, the photoelectric conversion layer20, the electrode layer24, an optical system84, a color variable layer82, and the voltage application unit44.

The second semiconductor region12of the silicon substrate16is connected to the reading circuit28through the source terminal70. Specifically, the second semiconductor region12is connected to the transfer transistor30of the reading circuit28. On the surface opposite the silicon substrate16of the reading circuit28, the insulation layer74is stacked in such a manner that the insulation layer74includes the wiring layers72provided on the surface.

The color variable layer82is disposed on the light incident side of the electrode layer24. The color variable layer82can sequentially switch reflection wavelengths in the red wavelength region, the green wavelength region, and the blue wavelength region by an applied voltage. The color variable layer82uses an electrostrictive effect of blue phases. Specifically, the color variable layer82sandwiches a blue phase by a pair of electrode layers. The pair of electrode layers is connected to the voltage application unit44. A spiral pitch of liquid crystal in the blue phase is changed by controlling an electric potential difference between the pair of electrode layers, thereby sequentially controlling the selective reflection wavelength in the red wavelength region, the green wavelength region, and the blue wavelength region by an applied voltage.

A change speed of the spiral pitch of liquid crystal is sufficiently higher than a frame rate (180 Hz) that is three times faster than that of typical moving images (frame rate of 60 Hz). The voltage application unit44thus drives the color variable layer82at 180 Hz in synchronization with the reading circuit28. The voltage application unit44preferably reads the signal according to light in the red wavelength range, the signal according to light in the green wavelength range, and the signal according to light in the blue wavelength range in one frame period of 60 Hz so as to practically perform full color imaging in each 60-Hz interval.

Light in the wavelength range selectively reflected by the color variable layer82reaching each pixel region B of the electrode layer24through the optical system84, is photoelectrically converted by the photoelectric conversion layer20, and thereafter reaches the silicon substrate16. The movements of electrons in the silicon substrate16and the operation of the reading circuit28are the same as those in the first embodiment.

As described above, the imaging device100E in the embodiment can achieve the same effect as the first embodiment because the imaging device100E includes the termination layer22while the color variable layer82is provided.

Seventh Embodiment

The following describes applications of the semiconductor device10in the embodiments described above. The semiconductor device10in the embodiments described above is applicable to a semiconductor chip, a mobile terminal provided with the imaging device100, and a vehicle provided with the imaging device100.

FIG. 11is a schematic diagram illustrating an example of a semiconductor chip90. The semiconductor chip90includes a substrate92on which the semiconductor device10is mounted. The semiconductor chip90includes the semiconductor device10in the embodiments described above.

The semiconductor chip90can thus obtain a signal from which noise is eliminated.

FIG. 12is a schematic diagram illustrating an example of a mobile terminal94. The mobile terminal94includes a main body96on which the semiconductor chip90is mounted as the imaging device100. The semiconductor chip90includes the semiconductor device10in the embodiments described above.

The mobile terminal94on which the semiconductor chip90is mounted can thus obtain a taken image from which noise is eliminated.

FIG. 13is a schematic diagram illustrating an example of a vehicle99. The vehicle99includes a vehicle body98on which the semiconductor chip90provided with the semiconductor device10is mounted as the imaging device100. The vehicle99on which the semiconductor chip90is mounted can thus obtain a taken image from which noise is eliminated.