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Patent Issued for Solid-State Imaging Device, Method of Driving Solid-State Imaging Device, and Camera

June 4, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- Panasonic Corporation (Osaka, JP) has been issued patent number 8730366, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventors are Yonemura, Koichi (Kyoto, JP); Shiraki, Hirokazu (Kyoto, JP); Tsukamoto, Akira (Osaka, JP).

This patent was filed on September 11, 2012 and was published online on May 20, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "Hereinafter, CCD solid-state imaging devices in the related art will be described with reference to the drawings.

"Recently, in solid-state imaging devices, the number of pixels in the horizontal direction has been increased in order to meet a demand for higher resolution. This results in a higher driving rate of a horizontal CCD register (horizontal transfer unit), causing problems such as reduction in transfer efficiency and increase in electricity consumption. As a method for solving such problems, techniques for providing a plurality of horizontal transfer units arranged in parallel have been reported (for example, see Patent Literatures 1 and 2).

"In the solid-state imaging device described in Patent Literature 1, the shape of a storage electrode in a horizontal transfer unit for performing branch transfer is devised, or the concentration of impurities on the branch transfer unit side (in the vertical transfer direction) is increased in the horizontal transfer unit for performing branch transfer. Thereby, a potential gradient is formed in the vertical transfer direction to suppress branch transfer failure. Unfortunately, in these structures, the potential gradient is always formed under a horizontal electrode. This causes various problems: the saturated charge amount in the horizontal transfer unit is reduced; or signal charges are horizontally transferred in a meandering manner during horizontal transfer to increase an effective transfer length per transfer stage, resulting in transfer failure.

"In order to improve such problems, the solid-state imaging device described in Patent Literature 2 includes a storage electrode in a horizontal transfer unit for performing branch transfer wherein the storage electrode includes a plurality of electrode elements, and charges are transferred by applying a different driving pulse to each of the electrode elements during branch transfer.

"FIG. 19 is a configuration diagram showing part of a horizontal transfer unit of a solid-state imaging device in the related art, which is described in Patent Literature 2. FIG. 20 is a potential schematic view showing a cross-sectional structure of a topmost layer of the horizontal transfer unit taken along the line B-B' shown in FIG. 19, and potential distributions and transfer states of signal charges under the respective electrodes. FIG. 21 is a drawing showing a timing at which the respective transfer pulses are applied to the corresponding electrodes in FIG. 19 during a horizontal blanking period. FIG. 20 shows the potential distributions and transfer states of signal charges under the respective electrodes during Periods N1 to N5 in FIG. 21.

"The solid-state imaging device described in Patent Literature 2 includes a channel stop 201, an intermediate transfer unit 206, a final vertical transfer electrode 207, horizontal storage electrodes 209 and 211, a horizontal barrier electrode 210, and a barrier region 213 as shown in FIG. 19. The horizontal storage electrodes 209 and 211 and the horizontal barrier electrode 210 form a horizontal transfer electrode. The horizontal transfer electrode has a structure for horizontal two-phase drive in which voltages .phi.H1 and .phi.H2A (.phi.H2B) are applied to the corresponding electrodes during the horizontal transfer to transfer the signal charges via a channel 215 provided in a semiconductor substrate 214 shown in FIG. 20.

"The horizontal storage electrode 211 transfers the signal charges from a first horizontal transfer unit 204 to a second horizontal transfer unit 205, and includes a first electrode element 211A and a second electrode element 211B. The first electrode element 211A covers substantially the center of the channel in the first horizontal transfer unit 204, the intermediate transfer unit 206, and the channel in the second horizontal transfer unit 205, and forms a storage electrode for the first horizontal transfer unit 204 and the second horizontal transfer unit 205. The second electrode element 211B covers the channel in the first horizontal transfer unit 204 not covered with the first electrode element 211A, and forms a storage electrode for the first horizontal transfer unit 204. The first electrode element 211A is electrically insulated from the second electrode element 211B. The second electrode element 211B has approximately the same width as that of the first electrode element 211A. As shown in FIG. 19, when observed from above, the second electrode element 211B is overlaid on the first electrode element 211A in a region ranging from the second horizontal transfer unit 205 to approximately a half region on a branch transfer electrode 208 in the first horizontal transfer unit 204.

"The storage electrode for the second horizontal transfer unit 205 is composed of only the first electrode element 211A, while the storage electrode for the first horizontal transfer unit 204 is composed of the second electrode element 211B covering approximately a half of the first horizontal transfer unit 204 on the side of the final vertical transfer electrode 207 and the first electrode element 211A covering approximately a half of first horizontal transfer unit 204 on the side of the intermediate transfer unit 206.

"The second electrode element 211B and the horizontal barrier electrode 210 are commonly connected while the first electrode element 211A is independently connected to an outside.

"Hereinafter, transfer operation will be described using FIGS. 19 to 21. First, .phi.H1 to be applied to the horizontal storage electrode 209 and .phi.H2A and .phi.H2B to be applied to the horizontal storage electrode 211 (first electrode element 211A, second electrode element 211B) are simultaneously set to a high level, and .phi.VL to be applied to the final vertical transfer electrode 207 is set to a low level. Thereby, the signal charges accumulated under the final vertical transfer electrode 207 in a vertical transfer unit 202 (solid dot shown in FIG. 19) are transferred to under the horizontal storage electrode 209 and the horizontal storage electrode 211 (first electrode element 211A, second electrode element 211B) corresponding to the first horizontal transfer unit 204 (Period N1, FIG. 20(a)).

"Next, .phi.T to be applied to the branch transfer electrode 208 is set to the high level, .phi.H1 and .phi.H2B are set to the low level at the same time, and .phi.H2A is set to a middle level between the high level and the low level. Thereby, the signal charges are transferred to the intermediate transfer unit 206 (Period N2, FIG. 20(b)).

"Subsequently, .phi.H2A is set to the low level, and transfer of the signal charges to the branching channel is completed (Period N3 FIG. 20).

"Next, .phi.H1 is set to the high level, and .phi.T is set to the low level. Thereby, the signal charges in the intermediate transfer unit 206 are transferred to under the horizontal storage electrode 209 in the second horizontal transfer unit 205 (Period N4, FIG. 20(d)).

"Meanwhile, the signal charges transferred from the vertical transfer unit 203 (blank dot in FIG. 19) remain within the first horizontal transfer unit 204 during Periods N2 to N4. Thereby, the signal charges in the vertical transfer units 202 and 203 are branched to the first horizontal transfer unit 204 and the second horizontal transfer unit 205, and branch transfer is completed.

"Subsequently, one branch of the signal charges is horizontally transferred within the first horizontal transfer unit 204 to an output unit (not shown), and the other branch thereof is horizontally transferred within the second horizontal transfer unit 205 to an output unit (not shown)."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventors' summary information for this patent: "Technical Problem

"Recently, a full HD moving picture output (1920.times.1080) at a higher frame rate has been increasingly demanded of cameras using the CCD. In order to meet such a higher frame rate, the horizontal transfer unit needs to be driven at a higher rate. In this case, however, the transfer efficiency of the signal charges is reduced.

"Meanwhile, as a first feature of the solid-state imaging device in the related art described in Patent Literature 2 (FIG. 19), different driving pulses are applied to the first electrode element 211A and the second electrode element 211B, respectively, when the signal charges are transferred from the first horizontal transfer unit 204, which are formed by a multilayer gate process to form a four or more layers, to the intermediate transfer unit 206. Thereby, the potential gradient is formed in the first horizontal transfer unit 204 to strengthen a transfer electric field. By reducing a transfer distance to substantially a half, the transfer electric field can be strengthened to suppress the transfer failure of the signal charges.

"As a second feature, in the horizontal transfer after the branch transfer is completed, the same driving pulse is applied to the first electrode element 211A and second electrode element 211B formed by the multilayer gate process to form a four or more layers. Thereby, the channel potential is the same under the electrode element 211A and the electrode element 211B in the first horizontal transfer unit 204, and the two electrode elements 211A and 211B corporate and function as one electrode functions. Namely, it is configured so as to form no potential gradient during the horizontal transfer, and reduction in the saturated charge amount in the horizontal transfer unit and horizontal transfer failure described above are suppressed.

"Unfortunately, in the configuration in the related art, the potential gradient is inevitably produced. As shown in FIG. 19, the configuration in the related art is a configuration of a two-layer (composite layer) electrode in which the horizontal storage electrode 209 and the horizontal barrier electrode 210 are repeated in the horizontal direction. Further, in order to branch transfer the signal charges in the first horizontal transfer unit 204, the first electrode element 211A and the second electrode element 211B are independently formed. For this reason, the horizontal barrier electrode 210 adjacent to the second electrode element 211B needs to be formed on the first electrode element 211A and the second electrode element 211B. Accordingly, the electrode structure has a three-layer structure.

"Meanwhile, in the process to form a composite layer electrode, diffusion of impurities due to increase in the number of a heat treatment cannot be avoided, and distribution of impurities is difficult to control. Additionally, it is extremely difficult to form an insulating film having the same thickness under the respective electrodes, causing a difference in the thickness of the insulating film. FIGS. 22A to 22D are schematic views showing ordinary steps when a composite layered transfer electrode such as the solid-state imaging device in the related art is formed. First, as shown in FIG. 22A, a p type well 222 is formed within an n type semiconductor substrate 221, and an n type diffusion layer 223 in a transfer channel is formed on the surface of the n type semiconductor substrate 221. Next, as shown in FIG. 22B, an insulating film 224 is formed on the n type diffusion layer 223 using one or both of thermal oxidation and thermal CVD. Subsequently, a polycrystalline silicon film is formed on the insulating film 224 by low pressure CVD, and a resist pattern 227 is formed by photolithography in a predetermined region in which a first transfer electrode 225 is formed. Next, as shown in FIG. 22C, using the resist pattern 227 as a mask, a portion in a region 228 is dry etched until the insulating film 224 is completely exposed. During the dry etching, the surface of the insulating film 224 is also etched. As a result, the thickness of an insulating film 229 under the region 228 to be etched is undesirably made smaller than the thickness of an insulating film 230 under the transfer electrode 225. Subsequently, the resist pattern 227 is removed to form the transfer electrode 225. Next, as shown in FIG. 22D, an insulating film 231 and a second transfer electrode 226 are formed. As above, in the process to form a composite layer electrode, a difference is inevitably produced between the thickness of the insulating film 230 under the first transfer electrode 225 and the thickness of the insulating film 230 under the second transfer electrode 226. Thus, when the thickness of the insulating film provided under the transfer electrodes varies for each transfer electrode and the same voltage is applied to the respective transfer electrodes, the potentials under the transfer electrodes are different from each other and not equal even if the concentration of impurities in the n type diffusion layer in the transfer channel is the same. Namely, as in the structure in the related art, when the electrodes are independently formed in the first horizontal transfer unit 204 as the first electrode element 211A and the second electrode element 211B, the potential gradient is undesirably formed. As a result, reduction in the saturated charge amount in the horizontal transfer unit and horizontal transfer failure as described above are produced.

"Further, the configuration in the related art insufficiently demonstrates the effect in the CCD formed of a cell having a small pixel size in which the number of pixels is 10 M or more, causing the transfer failure.

"The horizontal transfer electrode having the configuration in the related art uses a two-phase drive system as in FIG. 19 in which two electrodes of the storage electrode and the barrier electrode are formed per pixel. This increases the number of gate layers from three layers to four layers, and complicates the process. When the pixel size is small, the horizontal length of the electrode is short. Accordingly, in order to ensure a necessary saturated charge amount, the horizontal transfer unit needs to be designed to have a wider width in the two-phase drive system.

"For example, when the pixel size is approximately 5.0 .mu.m and relatively large, the width of the horizontal transfer unit to ensure the necessary saturated charge amount may be approximately 10 to 20 .mu.m. When the pixel size is approximately 1.5 .mu.m, the width of the horizontal transfer unit needs to be approximately 40 to 50 .mu.m.

"In FIG. 19, the width of the first horizontal transfer unit 204 in the vertical direction is greatly enlarged. As a result, the transfer distance from the first horizontal transfer unit 204 to the second horizontal transfer unit 205 is extremely increased. Even if different transfer pulses are applied to the first electrode element 211A and the second electrode element 211B during the transfer from the first horizontal transfer unit 204 to the second horizontal transfer unit 205, the transfer electric field becomes extremely weak in the vicinity of the center portion of the first electrode element 211A and in the vicinity of the center portion of the second electrode element 2116 because the transfer distance is long.

"For this reason, part of the signal charges remains, causing the transfer failure. Even if the horizontal driving voltage is increased to strengthen the transfer electric field, the electric field can be strengthened in end portions of the respective electrodes, but little effect is produced on the electric field in the vicinity of the center portion of the electrode because the electrode length is long.

"In this case, increase in the horizontal driving voltage leads to dramatic increase in the electricity consumption. Moreover, the number of independent electrodes can be further increased within the first horizontal transfer unit 204, and the transfer distance per electrode can be shortened to suppress the transfer failure. This method, however, has a defect such as increase in the number of terminals to be controlled.

"The present invention aims at solving the problems in the related art, and an object of the present invention is to provide a solid-state imaging device in which transfer failure of signal charges is suppressed.

"Solution to Problem

"In order to achieve the object above, a solid-state imaging device according one embodiment of the present invention is a solid-state imaging device comprising: a plurality of photoelectric conversion units two-dimensionally arranged; a plurality of vertical transfer units, each of which is provided for a corresponding one of columns of the photoelectric conversion units, has a plurality of vertical transfer electrodes, and is configured to vertically transfer signal charges read from the photoelectric conversion units; a plurality of horizontal transfer units, each of which has a plurality of horizontal transfer electrodes, and is configured to horizontally transfer the signal charges transferred from the vertical transfer unit; and an intermediate transfer unit provided between the plurality of horizontal transfer units, having a branch transfer electrode, and configured to transfer the signal charges between the plurality of horizontal transfer units, wherein each of the horizontal transfer units includes a first horizontal transfer unit configured to receive the signal charges from the vertical transfer unit, and a second horizontal transfer unit configured to receive the signal charges from the first horizontal transfer unit, in the first horizontal transfer unit, one of the horizontal transfer electrodes includes a plurality of column direction electrodes that are disposed adjacent to one another in the vertical direction and transfer the signal charges via the intermediate transfer unit to the second horizontal transfer unit, and the plurality of vertical transfer electrodes, the plurality of horizontal transfer electrodes, and the branch transfer electrode are a single layer electrode.

"According to the configuration, the signal charges are transferred by one column of the horizontal transfer electrode. Thereby, the transfer path can be shortened, and an unnecessary transfer operation can be eliminated. Accordingly, also in a solid-state imaging device having a small pixel size, the transfer failure of signal charges can be suppressed. Moreover, the horizontal transfer electrode is a single layer electrode. Accordingly, the configuration of the electrode is simple, and short circuit between the electrodes can be suppressed.

"Here, each of the column direction electrodes may have a rectangular shape in which a horizontal length on a side of the vertical transfer unit is equal to a horizontal length on a side of the intermediate transfer unit.

"Moreover, each of the column direction electrodes may be formed to have a horizontal length on the side of the vertical transfer unit shorter than a horizontal length on the side of the intermediate transfer unit.

"According to the configuration, the horizontal length of the first horizontal transfer electrode on the side of the first vertical transfer unit is shortened. Thereby, when the signal charges are transferred from the first horizontal transfer unit to the intermediate transfer unit and the second horizontal transfer unit 4, a narrow channel effect can be enhanced, a potential gradient can be formed such that the potential on the side of the intermediate transfer unit is deep, and the transfer electric field can be further strengthened.

"Here, each of the column direction electrodes may be formed to have a predetermined angle in the horizontal direction at an interface between the column direction electrodes.

"Moreover, the second horizontal transfer unit may include the column direction electrode having the same configuration of the column direction electrode in the first horizontal transfer unit.

"According to the configuration, the signal charges can be efficiently transferred, and the transfer failure of signal charges can be further suppressed.

"Here, each of the horizontal transfer units may include three or more horizontal transfer electrodes to which three or more phases of a transfer pulse are applied, the three or more phases of a transfer pulse forming one transfer packet.

"According to the configuration, the signal charges are transferred by one column of the horizontal transfer electrode among the three or more horizontal transfer electrodes. Thereby, the transfer path can be shortened, and an unnecessary transfer operation can be eliminated. Accordingly, also in a solid-state imaging device having a small pixel size, the transfer failure of signal charges can be suppressed. Moreover, the signal charges are horizontally transferred by three or more phase drive using three or more horizontal transfer electrodes. Accordingly, no horizontal barrier electrode needs to be provided. Thereby, the signal charges can be transferred at a low amplitude voltage, preventing increase in electricity consumption of the solid-state imaging device.

"Here, the solid-state imaging device may include a transfer control unit configured to select one of the vertical transfer units that transfers the signal charges to the horizontal transfer unit corresponding to the selected vertical transfer unit, wherein each of the horizontal transfer units has three or more horizontal transfer electrodes to which three or more phases of a transfer pulse is applied, the three or more phases of a transfer pulse forming one transfer packet.

"According to the configuration, the signal charges are transferred by one column of the horizontal transfer electrode among three or more horizontal transfer electrodes. Thereby, the transfer path can be shortened, and an unnecessary transfer operation can be eliminated. Moreover, the number of terminals in a package can be reduced. Further, inter-electrode capacitance can be reduced. Low electricity consumption can be attained when the horizontal driving voltage is the same.

"Here, the vertical transfer unit may include a plurality of first vertical transfer units, each of which is provided for a corresponding one of columns of the photoelectric conversion units and is configured to transfer the signal charges from the corresponding column of the photoelectric conversion units; and a second vertical transfer unit provided adjacent to the first vertical transfer units in the vertical direction and including a horizontal series of m columns of the first vertical transfer unit, m being an integer of 2 or more.

"According to the configuration, m columns of the first vertical transfer unit are connected to the second vertical transfer unit. Thereby, the signal charges are sequentially transferred in unit of m columns to the first horizontal transfer unit. Thereby, the transfer path can be shortened, and an unnecessary transfer operation can be eliminated. Accordingly, also in a solid-state imaging device having a small pixel size, the transfer failure of signal charges can be suppressed.

"Here, one end of the second vertical transfer unit connected to the first vertical transfer unit and other end of the second vertical transfer unit on a side opposite to the first vertical transfer unit may be provided continuously with a portion of the first horizontal transfer unit corresponding to a position of the column direction electrode in the first horizontal transfer unit.

"According to the configuration, the second vertical transfer unit is provided continuously with the portion of the first horizontal transfer unit corresponding to the position of the column direction electrode. Accordingly, the transfer path of the signal charges can be further shortened, and an unnecessary transfer operation can be eliminated. Accordingly, also in a solid-state imaging device having a small pixel size, the transfer failure of signal charges can be suppressed.

"Here, the plurality of column direction electrodes may be independently provided in a position not corresponding to a position of any of the plurality of vertical transfer units.

"According to the configuration, the column direction electrode is independently provided in a position not corresponding to any of the plurality of vertical transfer units. Thereby, the signal charges are not directly transferred from the vertical transfer unit to the first horizontal transfer unit under the column direction electrode, and transfer by mistake of the signal charges from the first horizontal transfer unit to the second horizontal transfer unit can be prevented.

"Here, each of the horizontal transfer units may be composed of a repeating set of four horizontal transfer electrodes to which four phases of a transfer pulse are applied, the four phases of a transfer pulse forming one transfer packet, and the horizontal transfer electrode in the first horizontal transfer unit may be two-phase shifted from the horizontal transfer electrode in the second horizontal transfer unit in the horizontal direction, and the horizontal transfer electrode in the first horizontal transfer unit and the horizontal transfer electrode in the second horizontal transfer unit may be commonly wired.

"According to the configuration, the signal charges are transferred by one column of the horizontal transfer electrode among four or more horizontal transfer electrodes. Thereby, the transfer path can be shortened, and an unnecessary transfer operation can be eliminated. Moreover, the signal charges are horizontally transferred by four- or more phase drive using four or more horizontal transfer electrodes. Accordingly, no horizontal barrier electrode needs to be provided. Thereby, the signal charges can be transferred at a low amplitude voltage, preventing increase in electricity consumption of the solid-state imaging device.

"Moreover, in order to achieve the object above, a method of driving a solid-state imaging device according to one embodiment of the present invention is a method of driving a solid-state imaging device, wherein the solid-state imaging device includes: a plurality of photoelectric conversion units two-dimensionally arranged; a plurality of vertical transfer units, each of which is provided for a corresponding one of columns of the photoelectric conversion units, and configured to vertically transfer signal charges read from the photoelectric conversion unit; a plurality of horizontal transfer units, each of which has a plurality of horizontal transfer electrodes, and is configured to horizontally transfer the signal charges from the vertical transfer unit, the vertical transfer units being disposed in parallel in the vertical direction; and an intermediate transfer unit provided between the plurality of horizontal transfer units, and configured to transfer the signal charges between the plurality of horizontal transfer units, and each of the horizontal transfer units includes a first horizontal transfer unit configured to receive the signal charges from the vertical transfer unit, and a second horizontal transfer unit configured to receive the signal charges from the first horizontal transfer unit, and in the first horizontal transfer unit, one of the horizontal transfer electrodes includes a plurality of column direction electrodes that are disposed adjacent to one another in the vertical direction, and transfer the signal charges via the intermediate transfer unit to the second horizontal transfer unit, the method comprising: applying different transfer pulses to the plurality of column direction electrodes to form a potential gradient in the vertical direction, when the signal charges are transferred between the plurality of horizontal transfer units; and applying the same transfer pulse to the plurality of column direction electrodes to equalize a potential in the vertical direction, when the signal charges are horizontally transferred in the horizontal transfer unit.

"According to the configuration, a potential gradient can be provided within the horizontal transfer unit by applying different transfer pulses to the plurality of column direction electrodes. Thereby, the signal charges can be easily transferred. Thereby, the transfer failure of signal charges can be suppressed.

"Moreover, the present invention not only can be realized as a solid-state imaging device, but also may be realized as a camera including the solid-state imaging device above.

"According to the configuration, a camera having the features of the solid-state imaging device can be provided.

"Advantageous Effects of Invention

"The solid-state imaging device according to the present invention can suppress the transfer failure of signal charges."

For the URL and additional information on this patent, see: Yonemura, Koichi; Shiraki, Hirokazu; Tsukamoto, Akira. Solid-State Imaging Device, Method of Driving Solid-State Imaging Device, and Camera. U.S. Patent Number 8730366, filed September 11, 2012, and published online on May 20, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=63&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=3119&f=G&l=50&co1=AND&d=PTXT&s1=20140520.PD.&OS=ISD/20140520&RS=ISD/20140520

Keywords for this news article include: Electronics, Semiconductor, Panasonic Corporation.

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