IMAGING ELEMENT AND IMAGING DEVICE

Imaging elements and imaging devices that reduce leakage of electric charges in a photoelectric conversion unit are disclosed. In one example, an imaging element includes photoelectric conversion units for generating an image signal corresponding to incident light. A charge retaining unit receives and retains sequentially transferred electric charges from the photoelectric conversion units. Charge transfer units are disposed for each of the photoelectric conversion units and transfer the electric charges to the charge retaining unit. Charge transfer signal lines are capacitively coupled to the charge retaining unit and are respectively connected to the charge transfer units to transmit a control signal. The charge transfer signal line connected to an earliest charge transfer unit that transfers the electric charges earliest in an image signal generation period is configured to have higher capacitance in the capacitive coupling than the other charge transfer signal lines.

FIELD

The present disclosure relates to an imaging element and an imaging device.

BACKGROUND

There has been used an imaging element configured by arranging, in a two-dimensional matrix, pixels each including a photoelectric conversion unit that performs photoelectric conversion of incident light. Besides the photoelectric conversion unit, a charge retaining unit that retaining electric charges generated by photoelectric conversion, a transfer transistor that transfers the electric charges of the photoelectric conversion unit to the charge retaining unit, and an image signal generation unit that generates an image signal according to the electric charges retained in the charge retaining unit are disposed in the pixel and the image signal is output.

An imaging element including a pixel in which a plurality of photoelectric conversion units are disposed in the pixel to share a charge retaining unit and an image signal generation circuit has been used. In this pixel, a transfer transistor is disposed for each of the plurality of photoelectric conversion units. In this pixel, electric charges generated by the plurality of photoelectric conversion units are sequentially transferred to the charge retaining unit and image signals are sequentially generated based on the transferred electric charges and output. Consequently, an increase in a pixel size can be reduced. In the imaging element including such a pixel, there has been proposed an imaging element that applies a predetermined voltage to a gate of a transfer transistor to thereby boost a charge retaining unit to improve charge transfer efficiency (see, for example, Patent Literature 1). In this imaging element, two sets of a photoelectric conversion units (photodiodes) and transfer transistors are disposed in the pixel. When one transfer transistor transfers electric charges, a predetermined intermediate voltage is applied to a gate of the other transfer transistor. Here, the intermediate voltage is a voltage intermediate between a high level for conducting the transfer transistor and a low level for making the transfer transistor nonconductive.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2018-121142 A

SUMMARY

Technical Problem

However, in the related art explained above, since the intermediate voltage is applied to the gate of the transfer transistor before the electric charges of the photoelectric conversion unit are transferred, there is a problem in that the electric charges of the photoelectric conversion unit leak and an error occurs in the image signal.

Therefore, the present disclosure proposes an imaging element and an imaging device that reduce electric charge leakage in a photoelectric conversion unit.

Solution to Problem

An imaging element according to the present disclosure includes: a plurality of photoelectric conversion units that are formed on a semiconductor substrate and performs photoelectric conversion of incident light in order to generate an image signal corresponding to the incident light; a charge retaining unit to which electric charges generated by the plurality of photoelectric conversion units in an image signal generation period, which is a period for generating the image signal after an exposure period for performing the photoelectric conversion in the plurality of photoelectric conversion units, are sequentially transferred and retained therein; a plurality of charge transfer units that are disposed for each of the plurality of photoelectric conversion units and conduct the photoelectric conversion unit and the charge retaining unit to thereby transfer the generated electric charges to the charge retaining unit; a plurality of charge transfer signal lines that are capacitively coupled to the charge retaining unit and are respectively connected to the plurality of charge transfer units to transmit a control signal; a reset unit that sequentially resets the charge retaining unit before the electric charges are sequentially transferred; and an image signal generation unit that sequentially generates the image signal based on the electric charges sequentially transferred and retained by the charge retaining unit in the image signal generation period, wherein the charge transfer signal line connected to an earliest charge transfer unit, which is the charge transfer unit that transfers the electric charges earliest in the image signal generation period among the plurality of charge transfer units, is configured to have higher capacitance in the capacitive coupling than the other charge transfer signal lines.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are explained in detail below with reference to the drawings. Explanation is made in the following order. Note that, in the embodiments explained below, redundant explanation is omitted by denoting the same parts with the same reference numerals and signs.1. First Embodiment2. Second Embodiment3. Third Embodiment4. Configuration of an imaging device

1. First Embodiment

Configuration of an Imaging Element

FIG.1is a diagram illustrating a configuration example of an imaging element according to an embodiment of the present disclosure. The figure is a block diagram illustrating a configuration example of an imaging element10. The imaging element10is a semiconductor element that generates image data of a subject. The imaging element10includes a pixel array unit11, a vertical drive unit12, a column signal processing unit13, and a control unit14.

The pixel array unit11is configured by arranging a plurality of pixels100. The pixel array unit11in the figure represents an example in which the plurality of pixels100are arranged in a shape of a two-dimensional matrix. Here, the pixel100includes a photoelectric conversion unit that performs photoelectric conversion of incident light. The pixel100generates an image signal of a subject based on irradiated incident light. For example, a photodiode can be used as the photoelectric conversion unit. Signal lines15and16are wired to each of the pixels100. The pixel100is controlled by a control signal transmitted by the signal line15to generate an image signal and outputs the generated image signal via the signal line16. Note that the signal line15is disposed for each of rows of the shape of the two-dimensional matrix and is wired in common to the plurality of pixels100disposed in one row. The signal line16is disposed for each of columns of the shape of the two-dimensional matrix and is wired in common to the plurality of pixels100disposed in in one column.

The vertical drive unit12generates the control signal for the pixel100explained above. The vertical drive unit12in the figure generates a control signal for each of the rows of the two-dimensional matrix of the pixel array unit11and sequentially outputs the control signal via the signal line15.

The column signal processing unit13processes the image signal generated by the pixel100. The column signal processing unit13in the figure simultaneously processes image signals from the plurality of pixels100disposed in one row of the pixel array unit11transmitted via the signal line16. As this processing, for example, analog-digital conversion for converting an analog image signal generated by the pixel100into a digital image signal and correlated double sampling (CDS) for removing an offset error of the image signal can be performed. The processed image signal is output to an external circuit or the like of the imaging element10.

The control unit14controls the vertical drive unit12and the column signal processing unit13. The control unit14in the figure outputs control signals respectively via signal lines17and18and controls the vertical drive unit12and the column signal processing unit13.

Note that the vertical drive unit12in the figure is an example of the drive circuit described in the claims. The imaging element10in the figure is an example of the imaging element described in the claims. The pixel array unit11in the figure can also be grasped as an example of the imaging element described in the claims. In this case, the column signal processing unit13is an example of the processing circuit described in the claims.

Configuration of the Pixel

FIG.2is a diagram illustrating a configuration example of the pixel according to the embodiment of the present disclosure. The figure is a circuit diagram illustrating a configuration example of the pixel100. The pixel100in the figure includes photoelectric conversion units101a,101b,101c,and101d,charge transfer units102a,102b,102c,and102d,a reset unit104, and an image signal generation unit110.

The image signal generation unit110includes MOS transistors105and106. The MOS transistors105and106, the charge transfer units102a,102b,102c,and102d,and the reset unit104can be configured by n-channel MOS transistors.

As explained above, the signal lines15and16are wired to the pixel100. The signal line15in the figure includes a charge transfer signal line TG1, a charge transfer signal line TG2, a charge transfer signal line TG3, a charge transfer signal line TG4, a reset signal line RST, and a selection signal line SEL. Besides, a power supply line Vdd is wired to the pixel100. The power supply line Vdd is a wire that supplies electric power to the pixel100.

An anode of the photoelectric conversion unit

101ais grounded and a cathode of the photoelectric conversion unit101ais connected to a source of the charge transfer unit102a.An anode of the photoelectric conversion unit101bis grounded and a cathode of the photoelectric conversion unit101bis connected to a source of the charge transfer unit102b.An anode of the photoelectric conversion unit101cis grounded and a cathode of the photoelectric conversion unit101cis connected to a source of the charge transfer unit102c.An anode of the photoelectric conversion unit101dis grounded and a cathode of the photoelectric conversion unit101dis connected to a source of the charge transfer unit102d.A drain of the charge transfer unit102a,a drain of the charge transfer unit102b,a drain of the charge transfer unit102c,and a drain of the charge transfer unit102dare connected in common to a gate of the MOS transistor105. A source of the reset unit104and one end of the charge retaining unit103are connected to the gate of the MOS transistor105. The other end of the charge retaining unit103is grounded. A drain of the MOS transistor105and a drain of the reset unit104are connected in common to the power supply line Vdd. A source of the MOS transistor105is connected to a drain of the MOS transistor106and a source of the MOS transistor106is connected to the signal line16.

The charge transfer signal line TG1, the charge transfer signal line TG2, the charge transfer signal line TG3, and the charge transfer signal line TG4are respectively connected to a gate of the charge transfer unit102a,a gate of the charge transfer unit102b,a gate of the charge transfer unit102c,and a gate of the charge transfer unit102d.The reset signal line RST and the selection signal line SEL are respectively connected to a gate of the reset unit104and a gate of the MOS transistor106.

The photoelectric conversion units101a,101b,101c,and101dperform photoelectric conversion of incident light. The photoelectric conversion units101a,101b,101c,and101dcan be configured by photodiodes formed on a semiconductor substrate120explained later.

The charge retaining unit103retains electric charges. The charge retaining unit103retains electric charges generated by the photoelectric conversion of the photoelectric conversion units101a,101b,101c,and101d. The charge retaining unit103can be configured by a floating diffusion (FD) region, which is a semiconductor region formed on the semiconductor substrate120.

The charge transfer units102a,102b,102c,and102dtransfer electric charges generated by the photoelectric conversion of the photoelectric conversion units101a,101b,101c,and101dto the charge retaining unit103. The charge transfer units102a,102b,102c,and102drespectively transfer the electric charges of the photoelectric conversion units101a,101b,101c,and101d. Control signals of the charge transfer units102a,102b,102c,and102dare respectively transmitted by the charge transfer signal lines TG1, TG2, TG3, and TG4. As the control signals, a voltage exceeding a threshold of a gate-source voltage Vgs of the MOS transistor configuring the charge transfer unit102aor the like (hereinafter referred to as ON voltage) can be used. By applying this ON signal to the gates of the charge transfer unit102aand the like, the charge transfer unit102aand the like can be conducted. Note that the gate-source voltage Vgs that brings the MOS transistors configuring the charge transfer unit102aand the like into a nonconductive state is referred to as OFF voltage. For example, 0 V or a negative polarity voltage corresponds to the OFF voltage.

The reset unit104resets the charge retaining unit103. This reset can be performed by conducting the charge retaining unit103and the power supply line Vdd to discharge electric charges of the charge retaining unit103. A control signal of the reset unit104is transmitted by the reset signal line RST. Note that, at the time of this reset, the photoelectric conversion unit101aand the like can also be reset by conducting the charge transfer unit102aand the like.

The image signal generation unit110generates an image signal based on the electric charges retained in the charge retaining unit103. As explained above, the image signal generation unit110is configured by the MOS transistors105and106. The gate of the MOS transistor105is connected to the charge retaining unit103. Therefore, an image signal having a voltage corresponding to electric charges retained by the charge retaining unit103is generated at the source of the MOS transistor105. By conducting the MOS transistor106, this image signal can be output to the signal line16. A control signal of the MOS transistor106is transmitted by the selection signal line SEL.

The ON voltage and the OFF voltage explained above can be applied to control signals for the reset unit104and the MOS transistor106as well.

The generation of the image signal in the pixel100in the figure can be performed as follows. First, the reset unit104and the charge transfer units102a,102b,102c,and102dare conducted. Consequently, electric charges of the photoelectric conversion units101a,101b,101c,and101dand the charge retaining unit103are discharged and reset. After the reset ends, an exposure period is started.

After a predetermined exposure period elapsed, the charge retaining unit103is reset by the reset unit104again. After the end of the reset, the charge transfer unit102ais conducted and electric charges of the photoelectric conversion unit101aare transferred to the charge retaining unit103and retained. An image signal corresponding to the retained electric charges is generated by the image signal generation unit110and output to the signal line16.

Next, a procedure from the reset of the charge retaining unit103to the output of the image signal is performed on the charge transfer units102b,102c,and102din order. Consequently, image signals based on the photoelectric conversion of the photoelectric conversion units101b,101c,and101dcan be output to the signal line16in order.

A period for generating an image signal after the exposure period is referred to as image signal generation period. As explained above, in this image signal generation period, electric charges generated by the photoelectric conversion unit101aand the like are transferred to the charge retaining unit103in the order of the charge transfer units102a,102b,102c,and102d. Among the charge transfer units, a charge transfer unit that transfers electric charges first is referred to as earliest charge transfer unit. In the example explained above, the charge transfer unit102acorresponds to the earliest charge transfer unit. As explained with reference toFIG.2, the charge transfer signal lines TG1, TG2, TG3, and TG4are connected to the charge transfer units102a,102b,102c,and102dand a control signal is transmitted.

Configuration of a Plane of the Pixel

FIG.3is a plan view illustrating a configuration example of a pixel according to the first embodiment of the present disclosure. The figure is a plan view illustrating a configuration example of the pixel100.

A region surrounded by an alternate long and short dash line in the figure represents a semiconductor region disposed on a semiconductor substrate (the semiconductor substrate120explained below) . A hatched region represents a gate electrode of a MOS transistor. A dot-hatched rectangle represents a contact plug (a contact plug149) explained below.

In the semiconductor substrate120, the photoelectric conversion units101a,101b,101c,and101dare disposed side by side in 2 rows and 2 columns. The photoelectric conversion units101a,101b,101c,and101dare respectively configured by semiconductor regions121a,121b,121c,and121d.

The charge retaining unit103is disposed in the center of the photoelectric conversion units101a,101b,101c,and101d.The charge retaining unit103is configured by a semiconductor region122.

The charge transfer units102a,102b,102c,and102dare respectively disposed between the photoelectric conversion units101a,101b,101c,and101dand the charge retaining unit103. In the figure, a gate electrode131a, a gate electrode131b,a gate electrode131c,and a gate electrode131dof the charge transfer units102a,102b,102c,and102dare illustrated.

The reset unit104is disposed adjacent to the left side of the photoelectric conversion unit101ain the figure. The reset unit104in the figure includes semiconductor regions124and123and a gate electrode132. The semiconductor regions124and123respectively configure a drain region and a source region, respectively. The MOS transistors105and106of the image signal generation unit110are disposed adjacent to the upper side of the photoelectric conversion unit101aand the charge transfer unit102bin the figure. The MOS transistor105includes semiconductor regions124and125and a gate electrode133. The MOS transistor106includes semiconductor regions125and126and a gate electrode134. The MOS transistor105shares a drain region with the reset unit104. The power supply line Vdd explained with reference toFIG.2is connected to the drain region. A source region of the MOS transistor105corresponds to a drain region of the MOS transistor106as well.

Configuration of a Cross Section of the Pixel

FIG.4is a sectional view illustrating a configuration example of the pixel according to the embodiment of the present disclosure. The figure is a diagram illustrating a simplified configuration of a cross section of the pixel100and is a diagram schematically illustrating a part of the pixel100. The pixel100includes a semiconductor substrate120, a wiring region140, insulating films129and160, a color filter170, and an on-chip lens180.

The semiconductor substrate120is a semiconductor substrate on which a diffusion region of the element of the pixel100is formed. The semiconductor substrate120can be made of silicon (Si). These semiconductor elements are formed in a well region of the semiconductor substrate120. For convenience, the semiconductor substrate120in the figure is assumed to configure a p-type well region. The diffusion region of the element can be disposed by forming an n-type or p-type semiconductor region in the well region. In the figure, the photoelectric conversion units101aand101d,the charge transfer units102aand102d,and the charge retaining unit103are illustrated among the elements configuring the pixel100. A white rectangle illustrated in the semiconductor substrate120represents an n-type semiconductor region. In the figure, n-type semiconductor regions121a,121d,and122are illustrated.

The photoelectric conversion unit101ais configured by the n-type semiconductor region121a. Specifically, a photodiode configured by pn junction at an interface between the n-type semiconductor region121aand a surrounding p-type well region corresponds to the photoelectric conversion unit101a.In the photoelectric conversion unit101a,electrons of electric charges generated by photoelectric conversion are accumulated in the n-type semiconductor region121aand transferred by the charge transfer unit102a.Similarly, the photoelectric conversion unit101dincludes an n-type semiconductor region121dand electrons of electric charges generated by photoelectric conversion are accumulated in the n-type semiconductor region121d.The electric charges are transferred by the charge transfer unit102d.The photoelectric conversion units101band101ccan also adopt the same configuration.

The charge retaining unit103is configured by an n-type semiconductor region122having a relatively high impurity concentration. The n-type semiconductor region122corresponds to the FD explained above.

Gate electrodes131aand131dconfiguring MOS transistors are disposed adjacent to the semiconductor substrate120. Note that a gate insulating film is disposed between the gate electrodes131aand131dand the semiconductor substrate120.

The charge transfer unit102ais configured by the n-type semiconductor region121acorresponding to a source region, the n-type semiconductor region122corresponding to a drain region, and the gate electrode131a. The charge transfer unit102dis configured by the n-type semiconductor region121dcorresponding to a source region, the n-type semiconductor region122corresponding to a drain region, and the gate electrode131d.The charge transfer unit102band the charge transfer unit102ccan also adopt a similar configuration.

The wiring region140includes a wire that is disposed on the front side of the semiconductor substrate120and transmits a signal to the element and an insulating layer141that insulates the wire. In the wiring region140in the figure, wires142and143are illustrated as the wire. The wire142is a wire connected to the charge retaining unit103. The wire142is a wire disposed in the bottom layer of the wiring region140. As described later, the wire142is a wire stopped inside the pixel100. In contrast, the wire143is a wire disposed above the wire142. The wire143is a wire extending to the outside of the pixel100as well. The wire143in the figure is connected to the gate electrodes131aand131dof the charge transfer units102aand102d.

The wires142and143can be made of metal such as copper (Cu). The insulating film129can be made of an insulator such as silicon oxide (SiO2) . The wire143and the gate electrode131aand the like can be connected by a contact plug149made of columnar metal. The wire142and the semiconductor region122can also be connected by the contact plug149.

The insulating film129is a film that insulates the surface on the front side of the semiconductor substrate120. Note that the insulating film129right under the gate electrode131aand the like configures the gate insulating film explained above. The insulating film160is a film that insulates the surface on the rear side of the semiconductor substrate120. The insulating films129and160can be made of, for example, SiO2.

The color filter170is an optical filter that transmits light having a predetermined wavelength in incident light. As the color filter170, for example, a color filter that transmits red light, green light, and blue light can be used.

The on-chip lens180is a lens that condenses incident light. The on-chip lens180is formed in, for example, a hemispherical shape and condenses incident light on the photoelectric conversion unit101aand the like.

The charge transfer signal lines TG1, TG2, TG3, and TG4explained with reference toFIG.2can be configured by the wire143. On the other hand, the wire142constitutes a charge retaining unit signal line. The charge retaining unit signal line is a signal line connected to the semiconductor region122configuring the charge retaining unit103, specifically, a signal line connected to the gate of the MOS transistor105and the source of the reset unit104.

Since the charge transfer signal lines TG1, TG2, TG3, and TG4are disposed near the charge retaining unit103, the charge transfer signal lines TG1, TG2, TG3, and

TG4are capacitively coupled to the charge retaining unit103. In the figure, the charge transfer signal lines TG1, TG2, TG3, and TG4are capacitively coupled to the charge retaining unit103via the wire142configuring the charge retaining unit signal line. As explained below, the charge transfer signal line TG1connected to the charge transfer unit102acorresponding to the earliest charge transfer unit has higher capacitance in the capacitive coupling explained above than the other charge transfer signal lines TG2, TG3, and TG4. This state is explained with reference toFIG.5.

Configuration of the Wires of the Pixel

FIG.5is a diagram illustrating a configuration example of the wires of the pixel according to the embodiment of the present disclosure. The figure is a plan view illustrating a configuration example of the wires of the pixel100. The figure is a diagram in which the wires142and143are illustrated over the pixel100illustrated inFIG.3. In the figure, description of a part of reference numerals is omitted. In the figure, dotted rectangles represent the wires143. “SEL” and “RST” of the wires143respectively represent the wires143configuring the selection signal line SEL and the reset signal line RST. “TG1”, “TG2”, “TG3”, and “TG4” of the wires143respectively represent the wires143configuring the charge transfer signal line TG1, the charge transfer signal line TG2, the charge transfer signal line TG3, and the charge transfer signal line TG4. Note that these signal lines are wired in common to the pixels100adjacent to each other.

The selection signal line SEL is connected to the gate electrode134of the MOS transistor106via the contact plug149. The reset signal line RST is connected to the gate electrode132of the reset unit104via the contact plug149. The charge transfer signal line TG1is connected to the gate electrode131aof the charge transfer unit102avia the contact plug149. The charge transfer signal line TG2is connected to the gate electrode131bof the charge transfer unit102bvia the contact plug149. The charge transfer signal line TG3is connected to the gate electrode131cof the charge transfer unit102cvia the contact plug149. The charge transfer signal line TG4is connected to the gate electrode131dof the charge transfer unit102dvia the contact plug149.

In the figure, a right-downward oblique line hatched region represents the wire142constituting the charge retaining unit signal line. As illustrated in the figure, the wire142is connected to the charge retaining unit103, the semiconductor region123configuring a source region of the reset unit104, and the gate electrode133of the MOS transistor105via the contact plug149. As illustrated in the figure, since the MOS transistor105and the reset unit104are disposed near the charge transfer unit102a,the wire143configuring the charge retaining unit signal line is also disposed near the charge transfer unit102a.Therefore, the capacitance between the gate electrode131aof the charge transfer unit102aand the wire142configuring the charge retaining unit signal line is higher than the capacitance of the charge transfer units102bto102d.That is, the coupling capacitance between the charge retaining unit103and the charge transfer signal line TG1is larger compared with the coupling capacitance among the other charge transfer signal lines TG2to TG4.

As explained above, when a charge transfer unit102and the like are conducted in order to transfer electric charges, an ON voltage is applied to a gate electrode131and the like of the charge transfer unit102and the like via the charge transfer signal line TG1and the like. Since the gate electrode131and the like and the charge retaining unit103are capacitively coupled, the charge retaining unit103is boosted by the ON voltage applied to the gate electrode131and the like of the charge transfer unit102and the like, potential rises, and the potential becomes deep. Consequently, electric charge transfer efficiency from a photoelectric conversion unit101and the like to the charge retaining unit103can be improved. In particular, since the charge transfer unit102ahas high coupling capacitance of the charge retaining unit103, the effect of boosting the charge retaining unit103is higher compared with the other charge transfer units102(the charge transfer units102bto102d) . Therefore, when the charge transfer units102bto102dtransfer electric charges, it is possible to assist the boosting of the charge retaining unit103by applying a predetermined voltage (a boosting voltage Vb explained below) to the charge transfer signal line TG1connected to the charge transfer unit102a.This state is explained with reference toFIGS.6A to6C.

Electric Charge Transfer

FIGS.6A to6Care diagrams illustrating an example of electric charge transfer according to the embodiment of the present disclosure. The figure is a diagram representing an example of electric charge transfer in the pixel100. The figure is a diagram illustrating potentials of the photoelectric conversion units101aand101b,the charge transfer units102aand102b,and the charge retaining unit103.

FIG.6Ais a diagram illustrating potential after elapse of an exposure period. Electric charges generated by photoelectric conversion are accumulated in the photoelectric conversion units101aand101b.Dot-hatched regions in the figure represents the accumulated electric charges. In the figure, an OFF voltage Voff is applied to the charge transfer signal lines TG1and TG2. Therefore, the charge transfer units102aand102bcome into a nonconductive state and have shallow potential.

FIG.6Bis a diagram illustrating potential at the time when the charge transfer unit102atransfers the electric charges of the photoelectric conversion unit101a. An arrow in the figure represents charge transfer. The On voltage Von is applied to the charge transfer signal line TG1, the charge transfer unit102acomes into a conductive state, and the potential becomes deeper than the potential of the photoelectric conversion unit101a.At this time, the charge retaining unit103capacitively coupled to the charge transfer signal line TG1is boosted and the potential becomes deeper. An electric field extending from the photoelectric conversion unit101ato the charge retaining unit103rises and the charge transfer efficiency can be improved.

FIG.6Cis a diagram illustrating potential at the time when the charge transfer unit102btransfers electric charges of the photoelectric conversion unit101b. The ON voltage Von is applied to the charge transfer signal line TG2, the charge transfer unit102bcomes into a conductive state, and the potential becomes deeper than the potential of the photoelectric conversion unit101b.The charge retaining unit103capacitively coupled to the charge transfer signal line TG2is boosted. At this time, the boosting voltage Vb is applied to the charge transfer signal line TG1. The boosting voltage is a voltage for boosting the charge retaining unit103. For example, a substantially intermediate voltage between the ON voltage and the OFF voltage can be applied. Specifically, when the ON voltage is 3 V and the OFF voltage is −1.2 V, a voltage of 1.8 V can be adopted as the boosting voltage Vb. By applying the boosting voltage Vb to the charge transfer signal line TG1, the charge retaining unit103is further boosted to be set to substantially the same potential as the potential illustrated inFIG.6B. Consequently, the charge transfer unit102bcan obtain the same transfer efficiency as the transfer efficiency of the charge transfer unit102a.

The potential of the charge transfer unit102abecomes deeper according to the application of the boosting voltage Vb. However, since the electric charges have been transferred by the charge transfer unit102a,the electric charges accumulated in the photoelectric conversion unit101ais substantially 0. Therefore, electric charge leakage from the photoelectric conversion unit101ato the charge retaining unit103does not occur. This driving procedure is applied to the charge transfer units102cand102das well.

By increasing the coupling capacitance between the charge transfer signal line TG1of the charge transfer unit102aand the charge retaining unit103in this way, the charge retaining unit103can be boosted when the ON voltage is applied to the charge transfer signal line TG1. Consequently, the electric charge transfer efficiency in the charge transfer unit102acan be improved. A boosting amount of the charge retaining unit103can be increased by superimposing a voltage by applying the boosting voltage Vb to the charge transfer signal line TG1at the time of the electric charge transfer in the charge transfer units102bto102d.Even if the coupling capacitance between the charge transfer signal lines TG2to TG4and the charge retaining unit103is small, the boosting of the charge retaining unit103at the time of the electric charge transfer is assisted, whereby the electric charge transfer efficiency in the charge transfer units102bto102dcan be improved.

Among the charge transfer signal lines TG1to TG4capacitively coupled to the charge retaining unit103, the charge transfer signal line TG1of the charge transfer unit102a,which is the earliest charge transfer unit, is configured to have higher coupling capacitance than the other charge transfer signal lines TG2to TG4. The electric charge transfer by the charge transfer unit102ais ended earliest. When the electric charges are transferred thereafter in the charge transfer units102bto102dto which the charge transfer signal lines TG2to TG4are connected, the boosting voltage Vb is applied to the charge transfer signal line TG1to assist the electric charge transfer. Consequently, the charge transfer efficiency in the charge transfer units102ato102dcan be substantially equalized. Note that the coupling capacitance to the charge retaining unit103in the charge transfer signal line TG1is preferably set to be 1.4 times the coupling capacitance of the other charge transfer signal lines TG2to TG4. This is because a proper boost amount of the charge retaining unit103can be obtained when the charge transfer units102bto102dtransfer electric charges.

Generation of an Image Signal

FIG.7is a diagram illustrating an example of generation of an image signal according to the first embodiment of the present disclosure. The figure is a timing chart illustrating an example of generation of an image signal in the pixel100. “SEL” and “RST” in the figure respectively represent signals of the selection signal line SEL and the reset signal line RST. “TG1”, “TG2”, “TG3”, and “TG4” respectively represent signals of the charge transfer signal line TG1, the charge transfer signal line TG2, the charge transfer signal line TG3, and the charge transfer signal line TG4. In these signals, a portion of a value “1” of a binarized waveform represents the ON voltage (Von) . As the ON voltage, for example, a voltage of 3 V can be applied. A portion of the value “0” represents the OFF voltage. A broken line in the figure represents a level of the OFF voltage. As the OFF voltage, for example, 0 V or a negative voltage (for example, −1.2 V) can be applied. “Vo” in the figure represents an image signal output to the signal line16.

In an initial state, the value “0” is input to the selection signal line SEL, the reset signal line RST, and the charge transfer signal lines TG1to TG4.

At T1, the ON voltage is input from the reset signal line RST and the charge transfer signal lines TG1to TG4. Consequently, the reset unit104and the charge transfer units102ato102dcome into a conductive state and the charge retaining unit103and the photoelectric conversion units101ato101dare reset.

At T2, the input of the ON voltage of the reset signal line RST and the charge transfer signal lines TG1to TG4is stopped. Consequently, the exposure period is started. Electric charges generated by photoelectric conversion in the photoelectric conversion units101ato101dare accumulated.

At T3, the exposure period ends. The ON voltage is input to the reset signal line RST and the reset unit104is conducted. Consequently, the charge retaining unit103is reset. The ON voltage is applied to the selection signal line SEL. Note that the application of the ON voltage to the selection signal line SEL is continued until T19. From T3, an image signal generation period, which is a period for generating an image signal in the pixel100, is started.

At T4, the input of the ON voltage to the reset signal line RST is stopped and the reset unit104comes into a nonconductive state. In a period of T4to T5, the image signal generation unit110generates an image signal A and outputs the image signal A to the signal line16. The image signal A corresponds to an image signal at a reset time.

At T5, the ON voltage (Von) is input from the charge transfer signal line TG1and the charge transfer unit102acomes into a conductive state. Consequently, electric charges accumulated in the photoelectric conversion unit101aare transferred to the charge retaining unit103.

At T6, the input of the ON voltage from the charge transfer signal line TG1is stopped and the charge transfer unit102acomes into a nonconductive state. In a period of T6to T7, the image signal generation unit110generates an image signal B and outputs the image signal B to the signal line16. The image signal B corresponds to an image signal based on electric charges of the photoelectric conversion unit101a.The CDS explained above can be performed by subtracting the image signal A from the image signal B.

At T7, the ON voltage is input to the reset signal line RST, the reset unit104is conducted, and the charge retaining unit103is reset.

At T8, the input of the ON voltage to the reset signal line RST is stopped. In a period of T8to T9, the image signal generation unit110generates an image signal C at the reset time and outputs the image signal C to the signal line16.

At T9, the ON voltage Von is input from the

charge transfer signal line TG2and the charge transfer unit102bcomes into a conductive state. Consequently, electric charges accumulated in the photoelectric conversion unit101bare transferred to the charge retaining unit103. The boosting voltage Vb is applied to the charge transfer signal line TG1and the charge retaining unit103is further boosted. For example, a voltage of 1.8 V can be applied as the boosting voltage Vb.

At T10, the input of the ON voltage from the charge transfer signal line TG2is stopped and the charge transfer unit102bcomes into a nonconductive state. The application of the boosting voltage Vb to the charge transfer signal line TG1is stopped. In a period of T10to T11, the image signal generation unit110generates an image signal D and outputs the image signal D to the signal line16. The CDS can be performed by subtracting the image signal C from the image signal D.

At T11, the ON voltage is input to the reset signal line RST, the reset unit104is conducted, and the charge retaining unit103is reset.

At T12, the input of the ON voltage to the reset signal line RST is stopped. In a period from T12to T13, the image signal generation unit110generates an image signal E at the reset time and outputs the image signal E to the signal line16.

At T13, the ON voltage Von is input from the charge transfer signal line TG3and the charge transfer unit102ccomes into a conductive state. Consequently, electric charges accumulated in the photoelectric conversion unit101care transferred to the charge retaining unit103. The boosting voltage Vb is applied to the charge transfer signal line TG1and the charge retaining unit103is further boosted.

At T14, the input of the ON voltage from the charge transfer signal line TG3is stopped and the charge transfer unit102ccomes into contact with a nonconductive state. The application of the boosting voltage Vb to the charge transfer signal line TG1is stopped. In a period of T14to T15, the image signal generation unit110generates an image signal F and outputs the image signal F to the signal line16. The CDS can be performed by subtracting the image signal E from the image signal F.

At T15, an ON voltage is input to the reset signal line RST, the reset unit104is conducted, and the charge retaining unit103is reset.

At T16, the input of the ON voltage to the reset signal line RST is stopped. In a period of T16to T17, the image signal generation unit110generates an image signal G at the reset time and outputs the image signal G to the signal line16.

At T17, the ON voltage Von is input from the charge transfer signal line TG4, and the charge transfer unit102dcomes into a conductive state. Consequently, electric charges accumulated in the photoelectric conversion unit101dis transferred to the charge retaining unit103. The boosting voltage Vb is applied to the charge transfer signal line TG1and the charge retaining unit103is further boosted.

At T18, the input of the ON voltage from the charge transfer signal line TG4is stopped and the charge transfer unit102dcomes into a nonconductive state. The application of the boosting voltage Vb to the charge transfer signal line TG1is stopped. In a period of T18to T19, the image signal generation unit110generates an image signal H and outputs the image signal H to the signal line16. The CDS can be performed by subtracting the image signal G from the image signal H.

At T19, the input of the ON voltage to the selection signal line SEL is stopped. At T19, the image signal generation period ends. According to the procedure explained above, an image signal can be generated in the pixel100.

Other Configurations of the Wires of the Pixel

FIGS.8to10are diagrams illustrating other configuration examples of the wires of the pixel according to the embodiment of the present disclosure. LikeFIG.5, the figures are plan views illustrating configuration examples of the wires of the pixel100. The pixel100illustrated inFIGS.8to10is different from the pixel100illustrated inFIG.5in the shape of the wire142.

FIG.8is a diagram illustrating an example in which the wire142extends a region near the gate electrode131a.The capacitance of the charge retaining unit103can be further increased by adding a region indicated by an alternate long and two dashes line in the figure.

FIG.9is a diagram illustrating an example in which a region where the charge transfer signal line TG1overlaps the wire142in a plan view is enlarged. In the pixel100illustrated in the figure, the charge transfer signal line TG1and the charge transfer signal line TG2are interchanged and disposed with respect toFIG.5and the wire142is disposed below the charge transfer signal line TG1in the region of the alternate long and two dashes line in the figure

InFIG.10, the gate electrode131ais extended to a region right under the wire142. As indicated by an alternate long and two dashes line in the figure, a region where the gate electrode131aand the wire142overlap can be enlarged.

Note that the configuration of the imaging element10is not limited to this example. For example, it is also possible to adopt a configuration in which eight photoelectric conversion units and eight charge transfer units are disposed in the pixel100.

As explained above, the imaging element10in the first embodiment of the present disclosure increases the coupling capacitance between the charge transfer signal line TG1of the charge transfer unit102a,which is the earliest charge transfer unit, and the charge retaining unit103. Consequently, the boosting amount of the charge retaining unit103at the time of application of the ON voltage to the charge transfer signal line TG1can be improved. The charge transfer efficiency of the charge transfer unit102acan be improved. By applying the boosting voltage Vb to the charge transfer signal line TG1at the time of transfer of electric charges in the charge transfer units102bto102d,the boosting amount of the charge retaining unit103can be increased and the charge transfer efficiency in the charge transfer units102bto102dother than the earliest charge transfer unit can be improved. At this time, since the electric charges of the photoelectric conversion unit101ahave been transferred, it is possible to prevent leakage of electric charges when the boosting voltage Vb is applied to the charge transfer unit102a,which is the earliest charge transfer unit.

2. Second Embodiment

The imaging element10of the first embodiment explained above applies the boosting voltage Vb to the charge transfer signal line TG1when the charge transfer units102bto102dtransfer electric charges. In contrast, the imaging element10in a second embodiment of the present disclosure is different from the imaging element10in the first embodiment in that the photoelectric conversion unit101ais reset every time the charge transfer units102bto102dtransfer electric charges.

Generation of an Image Signal

FIG.11is a diagram illustrating an example of generation of an image signal according to the second embodiment of the present disclosure. LikeFIG.7, the figure is a timing chart illustrating an example of generation of an image signal in the pixel100. The generation of the image signal in the figure is different from the generation of the image signal illustrated inFIG.7in that the photoelectric conversion unit101ais further reset when the charge retaining unit103is reset.

An ON signal is input to the charge transfer signal line TG1in the figure in a period in which the charge retaining unit103is reset. Specifically, the ON signal is input to the charge transfer signal line TG1in periods of T7to T8, T11to T12, and T15to T16in the figure. Therefore, the photoelectric conversion unit101ais also reset at the same time as the reset of the photoelectric conversion units101bto101d.Consequently, it is possible to discharge electric charges accumulated in the photoelectric conversion unit101aafter transfer of electric charges of the photoelectric conversion unit101ain T5to T6.

Depending on an amount of incident light on the imaging element10, the electric charges accumulated in the photoelectric conversion unit101aincrease and the electric charges leak when the boosting voltage Vb is applied to the charge transfer unit102a.Therefore, when the charge retaining unit103is reset, the photoelectric conversion unit101ais reset and the accumulated electric charges are discharged. Consequently, leakage of electric charges from the photoelectric conversion unit101acan be prevented.

Components of the imaging element10other than the above are the same as the components of the imaging element10in the first embodiment of the present disclosure. Therefore, explanation of the components is omitted.

As explained above, in the imaging element10in the second embodiment of the present disclosure, when the charge retaining unit103is reset, the photoelectric conversion unit101ais reset to discharge the accumulated electric charges. Consequently, it is possible to prevent leakage of electric charges from the photoelectric conversion unit101awhen the boosting voltage Vb is applied to the charge transfer signal line TG1. Noise and errors of image signals based on the photoelectric conversion units101bto101dcan be reduced.

The imaging element10of the first embodiment explained above applies the boosting voltage Vb to the charge transfer signal line TG1when the charge transfer units102bto102dtransfer electric charges. In contrast, the imaging element10in a third embodiment of the present disclosure is different from the imaging element10in the first embodiment explained above in that the boosting voltage Vb is applied to the charge transfer signal line TG1also in a period of formation of image signals in the photoelectric conversion units101bto101d.

Generation of an Image Signal

FIG.12is a diagram illustrating an example of generation of an image signal according to the third embodiment of the present disclosure. LikeFIG.7, the figure is a timing chart illustrating an example of generation of an image signal in the pixel100. The generation of the image signal illustrated in the figure is different from the generation of the image signal illustrated inFIG.7in that the boosting voltage Vb is applied to the charge transfer signal line TG1also in a period of formation of image signals in the photoelectric conversion units101bto101d.

In the charge transfer signal line TG1in the figure, a boosting voltage is applied to the charge transfer signal line TG1in periods of T8to T11, T12to T15, and T16to T19in the figure. Consequently, the boosting voltage Vb is applied to the gate (the gate electrode131a) of the charge transfer unit102ain a period of generation of image signals in the photoelectric conversion units101bto101d.An electric field between the gate and the drain of the charge transfer unit102acan be reduced and a leak current to the charge retaining unit103can be reduced.

Components of the imaging element10other than the above are the same as the components of the imaging element10in the first embodiment of the present disclosure. Therefore, explanation of the components is omitted.

As explained above, the imaging element10in the second embodiment of the present disclosure applies the boosting voltage Vb to the charge transfer signal line TG1also in the period of formation of image signals in the photoelectric conversion units101bto101d.Consequently, a leak current from a gate of a MOS transistor to the charge retaining unit103can be reduced and noise of an image signal can be reduced.

4. Configuration of an Imaging Device

The technique according to the present disclosure can be applied to various products. For example, the technique according to the present disclosure can be applied to an imaging device such as a camera.

FIG.13is a diagram illustrating a configuration example of an imaging device to which the technique according to the present disclosure can be applied. An imaging device1000illustrated in the figure includes an imaging element1001, a control unit1002, an image processing unit1003, a display unit1004, a recording unit1005, and a photographing lens1006.

The photographing lens1006is a lens that collects light from a subject. An image of the subject is formed on a light receiving surface of the imaging element1001by the photographing lens1006.

The imaging element1001is an element that images the subject. A plurality of pixels including photoelectric conversion units that perform photoelectric conversion of light from the subject is disposed on a light receiving surface of the imaging element1001. Each of the plurality of pixels generates an image signal based on electric charges generated by the photoelectric conversion. The imaging element1001converts an image signal generated by the pixel into a digital image signal and outputs the digital image signal to the image processing unit1003. Note that an image signal for one screen is referred to as frame. The imaging element1001can also output an image signal in units of frames.

The control unit1002controls the imaging element1001and the image processing unit1003. The control unit1002can be configured by, for example, an electronic circuit in which a microcomputer or the like is used.

The image processing unit1003processes the image signal from the imaging element1001. The processing of the image signal in the image processing unit1003corresponds to, for example, demosaic processing for generating an image signal of a color insufficient in generating a color image or noise reduction processing for removing noise of the image signal. The image processing unit1003can be configured by, for example, an electronic circuit in which a microcomputer or the like is used.

The display unit1004displays an image based on the image signal processed by the image processing unit1003. The display unit1004can be configured by, for example, a liquid crystal monitor.

The recording unit1005records an image (a frame) based on the image signal processed by the image processing unit1003. The recording unit1005can be configured by, for example, a hard disk or a semiconductor memory.

The imaging device to which the present disclosure can be applied is explained above. The present technique can be applied to the imaging element1001among the components explained above. Specifically, the imaging element10explained with reference toFIG.1can be applied to the imaging element1001. Note that the image processing unit1003is an example of the processing circuit described in the claims. The imaging device1000is an example of the imaging device described in the claims.

Note that the configuration of the second embodiment of the present disclosure can be applied to the other embodiments. Specifically, a driving method for further resetting the photoelectric conversion unit101awhen resetting the photoelectric conversion units101bto101dillustrated inFIG.11can be applied to the third embodiment of the present disclosure.

Effects

An imaging element includes a plurality of photoelectric conversion units, a charge retaining unit, a plurality of charge transfer units, a plurality of charge transfer signal lines, a reset unit, and an image signal generation unit. The plurality of photoelectric conversion units are formed on a semiconductor substrate and performs photoelectric conversion of incident light in order to generate an image signal corresponding to the incident light. Electric charges generated by the plurality of photoelectric conversion units in an image signal generation period, which is a period for generating the image signal after an exposure period for performing the photoelectric conversion in the plurality of photoelectric conversion units, are sequentially transferred to and retained in the charge retaining unit. The plurality of charge transfer units are disposed for each of the plurality of photoelectric conversion units and conduct the photoelectric conversion unit and the charge retaining unit to thereby transfer the generated electric charges to the charge retaining unit. The plurality of charge transfer signal lines are capacitively coupled to the charge retaining unit and are respectively connected to the plurality of charge transfer units to transmit a control signal. The reset unit sequentially resets the charge retaining unit before the electric charges are sequentially transferred. The image signal generation unit sequentially generates the image signal based on the electric charges sequentially transferred and retained by the charge retaining unit in the image signal generation period. The charge transfer signal line connected to an earliest charge transfer unit, which is the charge transfer unit that transfers the electric charges earliest in the image signal generation period among the plurality of charge transfer units, is configured to have higher capacitance in the capacitive coupling than the other charge transfer signal lines. Consequently, junction capacitance between the charge transfer signal line connected to the earliest charge transfer unit and the charge retaining unit can be increased.

The charge transfer unit may transfer the electric charges when an ON voltage formed by a MOS transistor and conducting itself is applied to a gate. The plurality of charge transfer signal lines may be respectively connected to gates of the plurality of charge transfer units and transmit, as the control signal, the ON voltage and an OFF voltage for bringing the charge transfer unit into a nonconductive state. Consequently, a control signal including the ON voltage and the OFF voltage is input to the charge transfer unit.

A boosting voltage for boosting the charge retaining unit may be applied to the gate of the earliest charge transfer unit when the other charge transfer units transfer the electric charges. The charge transfer signal line connected to the earliest charge transfer unit may transmit the control signal further including the boosting voltage. Consequently, the charge retaining unit can be boosted at the time of the charge transfer of the other charge transfer units.

The boosting voltage may be a substantially intermediate voltage between the ON voltage and the OFF voltage. Consequently, it is possible to prevent shift of the charge transfer unit to the conductive state while boosting the charge retaining unit.

The image signal generation unit may further generate an image signal at a reset time in a period from the reset in the reset unit to the transfer of the electric charges by the charge transfer unit. Consequently, an image signal due to the electric charges remaining in the charge retaining unit can be detected.

The boosting voltage may be further applied to the gate of the earliest charge transfer unit in a period in which an image signal at the reset time before the transfer of the electric charges by the other charge transfer units is generated and in a period in which the image signal after the transfer of the electric charges by the other charge transfer units is generated. Consequently, an electric field of the gate of the charge transfer unit can be reduced.

The ON voltage may be applied to the gate of the earliest charge transfer unit at the time of the reset by the reset unit before the transfer of the electric charges of the other charge transfer units. Consequently, the earliest charge transfer unit can discharge the electric charges of the photoelectric conversion unit corresponding thereto at the time of the transfer of the electric charges in the other charge transfer units.

The charge transfer signal line disposed near the charge retaining unit may be connected to the earliest charge transfer unit. Consequently, the coupling capacitance of the charge transfer signal line can be improved.

The imaging element may further include a charge retaining unit wire that connects the charge retaining unit and the image signal generation unit. The earliest charge transfer unit may be disposed near the charge retaining unit wire. Consequently, the coupling capacitance of the charge transfer signal line can be improved.

The charge retaining unit wire may be disposed below the charge retaining unit wire. Consequently, the coupling capacitance of the charge transfer signal line can be improved.

The imaging element may further include a drive circuit that outputs the control signal to the plurality of charge transfer signal lines.

An imaging device includes: a plurality of photoelectric conversion units that are formed on a semiconductor substrate and perform photoelectric conversion of incident light in order to generate an image signal corresponding to the incident light; a charge retaining unit that sequentially transfers and retains electric charges generated by the plurality of photoelectric conversion units in an image signal generation period, which is a period for generating the image signal after an exposure period in which the photoelectric conversion is performed in the plurality of photoelectric conversion units; a plurality of charge transfer units that are disposed for each of the plurality of photoelectric conversion units and transfer the generated electric charges to the charge retaining unit by conducting the photoelectric conversion unit and the charge retaining unit; a plurality of charge transfer signal lines capacitively coupled to the charge retaining unit and respectively connected to the plurality of charge transfer units to transmit a control signal; a reset unit that sequentially resets the charge retaining unit before the electric charges are sequentially transferred; an image signal generation unit that sequentially generates the image signal based on the electric charges sequentially transferred and retained in the charge retaining unit in the image signal generation period; and a processing circuit that processes the generated image signal, wherein the charge transfer signal line connected to an earliest charge transfer unit, which is the charge transfer unit that transfers the electric charges earliest in the image signal generation period among the plurality of charge transfer units, is configured to have higher capacitance in the capacitive coupling than other charge transfer signal lines. Consequently, junction capacitance between the charge transfer signal line connected to the earliest charge transfer unit and the charge retaining unit can be increased.

Note that the effects described in this specification are only illustrations and are not limited. Other effects may be present.

Note that the present technique can also take the following configurations.(1)An imaging element comprising:a plurality of photoelectric conversion units that are formed on a semiconductor substrate and performs photoelectric conversion of incident light in order to generate an image signal corresponding to the incident light;a charge retaining unit to which electric charges generated by the plurality of photoelectric conversion units in an image signal generation period, which is a period for generating the image signal after an exposure period for performing the photoelectric conversion in the plurality of photoelectric conversion units, are sequentially transferred and retained therein;a plurality of charge transfer units that are disposed for each of the plurality of photoelectric conversion units and conduct the photoelectric conversion unit and the charge retaining unit to thereby transfer the generated electric charges to the charge retaining unit;a plurality of charge transfer signal lines that are capacitively coupled to the charge retaining unit and are respectively connected to the plurality of charge transfer units to transmit a control signal;a reset unit that sequentially resets the charge retaining unit before the electric charges are sequentially transferred; andan image signal generation unit that sequentially generates the image signal based on the electric charges sequentially transferred and retained by the charge retaining unit in the image signal generation period, whereinthe charge transfer signal line connected to an earliest charge transfer unit, which is the charge transfer unit that transfers the electric charges earliest in the image signal generation period among the plurality of charge transfer units, is configured to have higher capacitance in the capacitive coupling than the other charge transfer signal lines.(2)The imaging element according to the above (1), whereinthe charge transfer unit transfers the electric charges when an ON voltage formed by a MOS transistor and conducting itself is applied to a gate, andthe plurality of charge transfer signal lines are respectively connected to gates of the plurality of charge transfer units and transmit, as the control signal, the ON voltage and an OFF voltage for bringing the charge transfer unit into a nonconductive state.(3)The imaging element according to the above (2), whereina boosting voltage for boosting the charge retaining unit is applied to the gate of the earliest charge transfer unit when the other charge transfer units transfer the electric charges, andthe charge transfer signal line connected to the earliest charge transfer unit transmits the control signal further including the boosting voltage.(4)The imaging element according to the above (3), wherein the boosting voltage is a substantially intermediate voltage between the ON voltage and the OFF voltage.(5)The imaging element according to the above (3), wherein the image signal generation unit further generates an image signal at a reset time in a period from the reset in the reset unit to the transfer of the electric charges by the charge transfer unit.(6)The imaging element according to the above (5), wherein the boosting voltage is further applied to the gate of the earliest charge transfer unit in a period in which an image signal at the reset time before the transfer of the electric charges by the other charge transfer units is generated and in a period in which the image signal after the transfer of the electric charges by the other charge transfer units is generated.(7)The imaging element according to any one of the above (2) to (6), wherein the ON voltage is applied to the gate of the earliest charge transfer unit at the time of the reset by the reset unit before the transfer of the electric charges of the other charge transfer units.(8)The imaging element according to any one of the above (1) to (8), wherein the charge transfer signal line disposed near the charge retaining unit is connected to the earliest charge transfer unit.(9)The imaging element according to any one of the above (1) to (8), further comprisinga charge retaining unit wire that connects the charge retaining unit and the image signal generation unit, whereinthe earliest charge transfer unit is disposed near the charge retaining unit wire.(10)The imaging element according to the above (9), wherein the charge retaining unit wire is disposed below the charge transfer signal line connected to the earliest charge transfer unit.(11)The imaging element according to any one of the above (1) to (10), further comprising a drive circuit that outputs the control signal to the plurality of charge transfer signal lines.(12)An imaging device comprising:a plurality of photoelectric conversion units that are formed on a semiconductor substrate and perform photoelectric conversion of incident light in order to generate an image signal corresponding to the incident light;a charge retaining unit that sequentially transfers and retains electric charges generated by the plurality of photoelectric conversion units in an image signal generation period, which is a period for generating the image signal after an exposure period in which the photoelectric conversion is performed in the plurality of photoelectric conversion units;a plurality of charge transfer units that are disposed for each of the plurality of photoelectric conversion units and transfer the generated electric charges to the charge retaining unit by conducting the photoelectric conversion unit and the charge retaining unit;a plurality of charge transfer signal lines capacitively coupled to the charge retaining unit and respectively connected to the plurality of charge transfer units to transmit a control signal;a reset unit that sequentially resets the charge retaining unit before the electric charges are sequentially transferred;an image signal generation unit that sequentially generates the image signal based on the electric charges sequentially transferred and retained in the charge retaining unit in the image signal generation period; anda processing circuit that processes the generated image signal, whereinthe charge transfer signal line connected to an earliest charge transfer unit, which is the charge transfer unit that transfers the electric charges earliest in the image signal generation period among the plurality of charge transfer units, is configured to have higher capacitance in the capacitive coupling than other charge transfer signal lines.

Reference Signs List