Depth pixel having multi-tab structure and time-of-flight sensor including the same

Abstract

To provide a time-of-flight sensor including range pixels.SOLUTION: The depth pixel PX of the ToF sensor may include a common photo gate CPG, a plurality of floating diffusion regions, a plurality of demodulating transfer gates TGA and TGB, and a plurality of overflow gates OG1 and OG2. The common photogate may be disposed in a central region of the depth pixel, and the plurality of floating diffusion regions may be disposed in a peripheral region PREG surrounding the central region. The plurality of demodulation transfer gates may be disposed in the peripheral region to be symmetrical with respect to each of a first horizontal line HLX and a second horizontal line HLY, which pass through a center of the depth pixel and are perpendicular to each other, such that the plurality of demodulation transfer gates transfer the photo-charges collected by the common photogate to the plurality of floating diffusion regions, respectively. A plurality of overflow gates are disposed in the peripheral region symmetrically with respect to each of the first and second horizontal lines to discharge the photocharges collected by the common photogate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to semiconductor integrated circuits, and more particularly to a range pixel having a multi-tab structure and a time-of-flight sensor including the range pixel. [Background technology]

[0002] Recently, with the growing interest in 3D sensing, which acquires the three-dimensional information of an object, various 3D cameras have been developed. Among the various types of 3D cameras, the Time of Flight (ToF) type camera is widely used due to its low circuit complexity and excellent distance resolution.

[0003] To extract distance information, a time-of-flight sensor uses a separate laser or light-emitting diode (LED) and a light source to illuminate a subject with modulated transmitted light, then measures the time difference or phase difference of the reflected light to calculate distance. The signal reflected back from the object is measured using a demodulated signal. To apply time-of-flight sensors to various electronic devices such as mobile devices, it is necessary to reduce the size and power consumption of time-of-flight sensors. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION In order to solve the above problems, an object of the present invention is to provide a range pixel capable of performing efficient distance measurement, and a time-of-flight sensor including the range pixel. [Means for solving the problem]

[0005] To achieve the above object, a range pixel of a time-of-flight sensor according to an embodiment of the present invention includes a common photogate, a plurality of floating diffusion regions, a plurality of demodulation transfer gates, and a plurality of overflow gates. The common photogate is disposed in a central region of a distance pixel, and the plurality of floating diffusion regions are disposed in an outer region surrounding the central region. The plurality of demodulation transfer gates are disposed in the outer region symmetrically with respect to first and second horizontal lines that pass through the center of the distance pixel and are perpendicular to each other, so as to transfer photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively. The plurality of overflow gates are disposed in the outer region symmetrically with respect to the first and second horizontal lines, so as to drain the photocharges collected by the common photogate.

[0006] To achieve the above object, a time-of-flight sensor according to an embodiment of the present invention includes a light source that irradiates a subject with modulated transmitted light, a sensing unit including one or more distance pixels and that provides distance information from the time-of-flight sensor to the subject based on received light reflected from the subject, and a control unit that controls the light source and the sensing unit. Each of the distance pixels includes a common photogate disposed in a central region of the distance pixel, a plurality of floating diffusion regions disposed in an outer region surrounding the central region, a plurality of demodulation transfer gates disposed in the outer region symmetrically with respect to first and second horizontal lines that pass through the center of the distance pixel and are perpendicular to each other, to transfer photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively, and a plurality of overflow gates disposed in the outer region symmetrically with respect to the first and second horizontal lines to discharge the photocharges collected by the common photogate.

[0007] Furthermore, to achieve the above-mentioned object, a range pixel of a time-of-flight sensor according to an embodiment of the present invention includes a common photogate arranged in a central region of the range pixel, a plurality of floating diffusion regions arranged in an outer region surrounding the central region, a plurality of demodulation transfer gates arranged in the outer region to transfer photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively, charge storage structures arranged in the outer region between the plurality of floating diffusion regions and the plurality of demodulation transfer gates to temporarily store the photocharges collected by the common photogate before transferring them to the plurality of floating diffusion regions, and a plurality of overflow gates arranged in the outer region to discharge the photocharges collected by the common photogate.

[0008] To achieve the above object, the distance pixel includes a common photogate disposed in a central region of the distance pixel, extending in a vertical direction perpendicular to the upper surface of the semiconductor substrate, and including one or more vertical photogates disposed inside one or more trenches formed in the upper region of the semiconductor substrate; a plurality of floating diffusion regions disposed in an outer region surrounding the central region; a plurality of demodulation transfer gates disposed in the outer region to transfer photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively; and one or more overflow gates disposed in the outer region to discharge the photocharges collected by the common photogate. [Effects of the Invention]

[0009] The range pixel according to the embodiment of the present invention can reduce the power consumption and size of the range pixel and the time-of-flight sensor that includes the range pixel by applying one common photogate.

[0010] In addition, the range pixel according to an embodiment of the present invention can improve the performance of the range pixel and the time-of-flight sensor including the range pixel by increasing the sensing accuracy and sensing sensitivity through a symmetrical structure and a modified structure of the common photogate. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 2a] 1 is a cross-sectional view showing a vertical structure of a distance pixel according to an embodiment of the present invention; [Figure 2b] 1 is a cross-sectional view showing a vertical structure of a distance pixel according to an embodiment of the present invention; [Figure 3a] 1 is a cross-sectional view showing a vertical structure of a distance pixel according to an embodiment of the present invention; [Figure 3b] 1 is a cross-sectional view showing a vertical structure of a distance pixel according to an embodiment of the present invention; [Figure 4] FIG. 1 is a circuit diagram illustrating a range pixel having a 2-tab structure according to an embodiment of the present invention. [Figure 5] FIG. 5 illustrates an example layout of a distance pixel having the two-tab structure of FIG. 4. [Figure 6] 5 is a timing diagram illustrating an example of the operation of the range pixel having the two-tab structure of FIG. 4. [Figure 7] 5 is a timing diagram illustrating an example of the operation of the range pixel having the two-tab structure of FIG. 4. [Figure 8] FIG. 1 is a circuit diagram showing a range pixel having a two-tub structure applying individual photogates. [Figure 9] FIG. 9 is a timing diagram illustrating the operation of the range pixel having the two-tab structure of FIG. 8. [Figure 10] FIG. 1 is a block diagram illustrating a time-of-flight sensor according to an embodiment of the present invention. [Figure 11] 10A and 10B are diagrams for explaining an example of measurement and calculation of the distance to a subject in a time-of-flight sensor. [Figure 12]10A and 10B are diagrams for explaining an example of measurement and calculation of the distance to a subject in a time-of-flight sensor. [Figure 13] FIG. 1 is a circuit diagram illustrating a range pixel having a 4-tab structure according to an embodiment of the present invention. [Figure 14] FIG. 14 shows an example layout of a distance pixel having the four-tab structure of FIG. 13. [Figure 15] FIG. 14 is a timing diagram illustrating one embodiment of the operation of the range pixel having the four-tab structure of FIG. 13. [Figure 16] FIG. 10 illustrates an embodiment of floating diffusion region sharing for range pixels according to an embodiment of the present invention. [Figure 17] FIG. 10 illustrates an embodiment of floating diffusion region sharing for range pixels according to an embodiment of the present invention. [Figure 18a] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 18b] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 18c] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 19a] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 19b] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 19c] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 20] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 21a] 21 is a perspective view showing an example of a common photogate included in the range pixel of FIG. 20. FIG. [Figure 21b] 21 is a perspective view showing an example of a common photogate included in the range pixel of FIG. 20. FIG. [Figure 22] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 23a]23 is a perspective view showing an example of a common photogate included in the range pixel of FIG. 22. FIG. [Figure 23b] 23 is a perspective view showing an example of a common photogate included in the range pixel of FIG. 22. FIG. [Figure 24] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 25] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 26] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 27] FIG. 2 illustrates a layout of a distance pixel according to an embodiment of the present invention. [Figure 28] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 29] FIG. 29 is a perspective view showing one embodiment of a common photogate included in the range pixel of FIG. 28. [Figure 30a] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 30b] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 30c] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 31a] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 31b] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 31c] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 32] 1 is a cross-sectional view illustrating a range pixel according to an embodiment of the present invention. [Figure 33a] 33A and 33B show examples of polarization structures included in the distance pixels of FIG. 32. [Figure 33b] 33A and 33B show examples of polarization structures included in the distance pixels of FIG. 32. [Figure 34] FIG. 1 is a block diagram showing an example in which the image sensor of the present invention is applied to a computer system. [Figure 35] FIG. 35 is a block diagram illustrating an example of an interface used in the computer system of FIG. 34. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The same reference numerals are used to designate the same components in the drawings, and redundant description of the same components will be omitted.

[0013] Figure 1 is a diagram showing the layout of a distance pixel according to an embodiment of the present invention, Figures 2a and 2b are cross-sectional views showing the vertical structure of a distance pixel according to an embodiment of the present invention, and Figures 3a and 3b are cross-sectional views showing the vertical structure of a distance pixel according to an embodiment of the present invention.

[0014] Hereinafter, two directions parallel to the upper surface of the substrate and intersecting each other are defined as a first horizontal direction (X) and a second horizontal direction (Y), respectively, and a direction substantially perpendicular to the upper surface of the substrate is defined as a vertical direction (Z). The first horizontal direction (X) corresponds to the row direction, and the second horizontal direction (Y) corresponds to the column direction.

[0015] As shown in Figures 1 to 3, a distance pixel (PX) includes a common photogate (CPG), multiple floating diffusion regions (FDA, FDB), multiple demodulation transfer gates (TGA, TGB), and multiple overflow gates (OG1, OG2). For ease of illustration and explanation, Figures 1 to 3 show two floating diffusion regions (FDA, FDB) and two demodulation transfer gates (TGA, TGB) corresponding to a two-tub structure, but the present invention is not limited to this example. The number of demodulation transfer gates and floating diffusion regions may vary depending on the number of tubs in the distance pixel (PX). The number of overflow gates may also vary.

[0016] A common photogate (CPG) is arranged in a central region (CREG) of the distance pixel (PX), and multiple floating diffusion regions (FDA, FDB), multiple demodulation transfer gates (TGA, TGB), and multiple overflow gates (OG1, OG2) are arranged in an outer region (PREG) surrounding the central region (CREG).

[0017] A plurality of demodulation transfer gates (TGA, TGB) transfer the photocharges collected by the common photogate (CPG) to a plurality of floating diffusion regions (FDA, FDB), and a plurality of overflow gates (OG1, OG2) drain the photocharges collected by the common photogate (CPG). The operation of the distance pixel (PX) will be described later with reference to Figures 6 and 7.

[0018] A plurality of demodulation transfer gates (TGA, TGB) are arranged in the outer region (PREG) symmetrically with respect to each of a first horizontal line (HLX) and a second horizontal line (HLY) that are perpendicular to each other through the center (CP) of the distance pixel (PX). Also, a plurality of overflow gates (OG1, OG2) are arranged in the outer region (PREG) symmetrically with respect to each of the first horizontal line (HLX) and the second horizontal line (HLY).

[0019] In one embodiment, as will be described later with reference to Figures 4 and 5, the distance pixel (PX) further includes charge storage structures disposed between the plurality of demodulation transfer gates (TGA, TGB) and the plurality of floating diffusion regions (FDA, FDB), respectively. The charge storage structures can temporarily store photocharges collected by the common photogate (CPG) before transferring them to the plurality of floating diffusion regions (FDA, FDB).

[0020] In general, a range pixel includes a plurality of photogates, and provides a plurality of demodulation signals having different phases to the plurality of photogates during an integration period for sensing the intensity of incident light. Meanwhile, a range pixel (PX) according to an embodiment of the present invention includes one common photogate (CPG) disposed in a central region (CREG). As will be described later with reference to FIGS. 6 and 7, during the integration period, a plurality of demodulation signals having different phases are provided to a plurality of demodulation transfer gates (TGA, TGB), respectively. During the integration period, A photogate voltage (VPG) applied to a common photogate (CPG) has a DC voltage level for collecting photocharges, and overflow gate voltages applied to the multiple overflow gates during the light collection period have a turn-off voltage level for blocking the discharge of the photocharges.

[0021] 2a and 2b, the distance pixel (PX) includes floating diffusion regions (FDA, FDB) and drain regions (DR1, DR2) formed on a semiconductor substrate 10, and a common photogate (CPG), demodulation transfer gates (TGA, TGB), and overflow gates (OG1, OG2) formed on the semiconductor substrate 10. The floating diffusion regions (FDA, FDB), drain regions (DR1, DR2), common photogate (CPG), demodulation transfer gates (TGA, TGB), and overflow gates (OG1, OG2) are arranged symmetrically with respect to a vertical line (VLZ) passing through the center (CP) of the pixel.

[0022] The floating diffusion regions (FDA, FDB) and drain regions (DR1, DR2) are formed in the semiconductor substrate 10 by an ion implantation process into the upper surface 11 of the semiconductor substrate 10, and the common photogate (CPG), demodulation transfer gates (TGA, TGB), and overflow gates (OG1, OG2) are formed separately from the semiconductor substrate 10 by a deposition process, an etching process, etc. An insulating layer (DL), such as an oxide film, is interposed between the upper surface 11 of the semiconductor substrate 10 and the gates (CPG, TGA, TGB, OG1, OG2).

[0023] The gates (CPG, TGA, TGB, OG1, OG2) may include polysilicon or transparent conducting oxide (TCO), for example, the gates (CPG, TGA, TGB, OG1, OG2) may include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), titanium oxide (TiO2), or a combination thereof.

[0024] Light incident on the distance pixel (PX) is incident from the upper surface of the semiconductor substrate 10, and in this case, the gates (CPG, TGA, TGB, OG1, OG2) are formed to include a transparent conductive oxide. On the other hand, light incident on the distance pixel (PX) is incident from the lower surface of the semiconductor substrate 10, and in this case, the gates (CPG, TGA, TGB, OG1, OG2) may include an opaque conductive oxide.

[0025] The distance pixel (PX) further includes a photocharge storage region (PD), such as a photodiode, doped with impurities of the opposite conductivity type to that of the semiconductor substrate 10 and formed in the semiconductor substrate 10 below the common photogate (CPG). That is, the photocharge storage region (PD) may be formed below the common photogate (CPG) so as to be separated from the floating diffusion regions (FDA, FDB) and the drain regions (DR1, DR2). In one embodiment, the semiconductor substrate 10 is a P-type substrate, and the photocharge storage region (PD) is doped with N-type impurities. In another embodiment, the semiconductor substrate 10 is an N-type semiconductor substrate or an N-type well formed in a P-type substrate, and the photocharge storage region (PD) is doped with P-type impurities.

[0026] A photogate voltage (VPG) is applied to the common photogate (CPG), and demodulation signals (STGA, STGB) are applied to the demodulation transfer gates (TGA, TGB), respectively. The demodulation signals (STGA, STGB) have mutually different phases, and during the light collection period, photocharges corresponding to the phases of the demodulation signals (STGA, STGB) are transferred to the floating diffusion regions (FDA, FDB), respectively.

[0027] An overflow gate voltage (VOG) is applied to the overflow gates (OG1, OG2), and a power supply voltage (VDD) is applied to the drain regions (DR1, DR2). During the light-focusing period, the overflow gate voltage (VOG) has a turn-off voltage level to block the discharge of photocharges collected by the common photogate (CPG). In periods other than the light-focusing period, the overflow gate voltage (VOG) has a turn-on voltage level to discharge the photocharges. In periods other than the light-focusing period, the turn-on voltage level forms a channel in the semiconductor substrate 10 between the photocharge storage region (PD) and the drain regions (DR1, DR2), and the collected photocharges are discharged to the power supply voltage (VDD) terminal. A global shutter function can be implemented using such overflow gates (OG1, OG2).

[0028] Time-of-Flight (TOF) optical sensing devices measure the light reflected from an object to calculate the distance to the object. To do this, a lock-in detection method using two tabs (2-tap) or four tabs (4-tap) corresponding to different phases is commonly used.

[0029] Generally, in lock-in detection, these tabs have a phase difference of 180 degrees (for two tabs) or 90 degrees (for four tabs) with the transmitted light irradiated on the subject, and a sine wave or pulse train signal with a duty cycle of 50% is used. For lock-in detection, a multi-tab distance pixel is used, in which the photocharge storage region and / or photocharge generation region is shared by multiple floating diffusion regions.

[0030] 2a and 2b, in the vertical structure of FIGS. 3a and 3b, the semiconductor substrate 10 includes multiple regions 13, 14, and 15 that are differentiated by being doped with impurities at different concentrations and / or different conductivity types. For example, if the semiconductor substrate 10 is of P-type conductivity, the semiconductor substrate 10 includes, from top to bottom, an N-region 13, a P-region 14, and a P+region 15. The P-region 14 is doped with impurities of the opposite conductivity type to the N-region 13, and the P+region 15 has a higher impurity concentration than the P-region 14. When near-infrared radiation (NIR) having a wavelength of 700 nm to 850 nm is used as the transmission light for the time-of-flight sensor, a P-type semiconductor substrate can be used rather than an N-type semiconductor substrate.

[0031] Photons incident on the distance pixel (PX) penetrate into the P-region 14 and generate electron-hole pairs. That is, the P-region 14 corresponds to the main photocharge generation region. The generated photoelectrons as minority carriers move to the depletion region of the NP junction, which corresponds to the boundary between the N-region 13 and the P-region 14, and are collected by the common photogate (CPG). At this time, since the P+region 15, which has a higher impurity concentration, is located below the P-region 14, photoelectrons generated near the boundary between the P-region 14 and the P+region 15 have a strong tendency to move to the NP junction region.

[0032] Depending on the embodiment, the N-region 13 can be replaced with a P-region, which may have a higher concentration than the P-region 14 to better block photoelectrons when the gates (CPG, TGA, TGB, OG1, OG2) are turned off and transmit only when the gates (CPG, TGA, TGB, OG1, OG2) are turned on.

[0033] The sensitivity of the unit pixel 100b can be further improved by forming a plurality of photocharge generation regions 13, 14, and 15, each differentiated by being doped with impurities at different concentrations, on the semiconductor substrate 10. Meanwhile, in addition to the plurality of photocharge generation regions 13, 14, and 15, a photocharge storage region (PD), such as the photodiode described above, is further formed.

[0034] Fig. 4 is a circuit diagram showing a distance pixel having a two-tab structure according to an embodiment of the present invention, and Fig. 5 is a diagram showing one embodiment of the layout of the distance pixel having the two-tab structure of Fig. 4. Below, explanations that overlap with those of Figs. 1 to 3 will be omitted.

[0035] As shown in Figures 4 and 5, the distance pixel (PX1) includes transistors (TMA, TS, TT) corresponding to the first tub (TA), transistors (TMB, TS, TT) corresponding to the second tub (TB), transistors (TRS, TSF, TSL) corresponding to the readout circuit, and a common photogate (CPG), overflow gates (OG1, OG2), and photodiode (PD) corresponding to the shared circuit.

[0036] Each of the transistors (TMA, TMB, TS, TT, TRS) includes a gate disposed on a semiconductor substrate, and a source region and a drain region formed on both sides of the gate on the semiconductor substrate. The gates of the transistors (TMA, TMB, TS, TT, TRS) correspond to a first demodulation transfer gate (TGA), a second demodulation transfer gate (TGB), a storage gate (SG), a FD transfer gate (TG), and a reset gate (RG), respectively.

[0037] A photogate voltage (VPG) is applied to the common photogate (CPG), an overflow gate voltage (VOG) is applied to the overflow gates (OG1, OG2), a storage control signal (SSG) is applied to the storage gate (SG), an FD transfer control signal (STG) is applied to the FD transfer gate (TG), a reset signal (SRG) is applied to the reset gate (RG), and a select signal (SEL) is applied to the gate of the select transistor (TSL). A first demodulation signal (STGA) and a second demodulation signal (STGB) having mutually different phases are applied to the first demodulation transfer gate (TGA) and the second demodulation transfer gate (TGB), respectively.

[0038] The photogate voltage (VPG), overflow gate voltage (VOG), storage control signal (SSG), FD transfer control signal (STG), reset signal (SRG), selection signal (SEL), and demodulation signals (STGA, STGB) are provided from the row scanning circuit 130 under the control of the control unit 150 in FIG. 10.

[0039] The storage gate (SG) is one of the charge storage structures and can temporarily store charge before transferring the charge to the floating diffusion region (FDA, FDB) via the demodulation transfer gate (TGA, TGB). In one embodiment, the charge storage structure is embodied as the storage gate (SG) alone. In another embodiment, the charge storage structure can be embodied as a structure in which a storage diode is further formed in the semiconductor substrate below the storage gate (SG). In this way, the inclusion of a charge storage structure in the distance pixel (PX1) enables accurate Correlated Double Sampling (CDS) operation and minimizes read noise. Depending on the embodiment, the FD transfer gate (TG) and / or the storage gate (SG) can be omitted.

[0040] The charges stored in the floating diffusion regions (FDA, FDB) are provided as output signals (VOUTA, VOUTB) via a transistor (TSF) that acts as a source follower buffer amplifier and a selection transistor (TSL).

[0041] As shown in FIG. 5, one common photogate (CPG) is disposed in the central region, and the demodulation transfer gates (TGA, TGB) and overflow gates (OG1, OG2) have a symmetrical structure with respect to the common photogate (CPG). The demodulation transfer gates (TGA, TGB) are disposed symmetrically with respect to the first horizontal line (HLX) and the second horizontal line (HLY), which are perpendicular to each other, passing through the center (CP) of the distance pixel (PX1). In other words, the first demodulation transfer gate (TGA) and the second demodulation transfer gate (TGC) are symmetrical with respect to the center of the distance pixel (PX1). In addition, the overflow gates (OG1, OG2) are disposed symmetrically with respect to the first horizontal line (HLX) and the second horizontal line (HLY). Such a symmetrical structure can reduce characteristic deviations between multiple tubs and improve the sensing accuracy of the distance pixels.

[0042] 6 and 7 are timing diagrams illustrating an example of the operation of the range pixel having the two-tab structure of FIG.

[0043] As shown in FIGS. 4 to 7, during the light concentration interval (TINT), a photogate voltage (VPG) applied to the common photogate (CPG) has a DC voltage level (VDC) for collecting photocharges, and an overflow gate voltage (VOG) applied to the overflow gates (OG1, OG2) during the light concentration interval (TINT) has a turn-off voltage level (VOFF) for blocking the discharge of the photocharges. Also, during the light concentration interval (TINT), a first demodulation signal (STGA) and a second demodulation signal (STGB) having different phases are applied to the first demodulation transfer gate (TGA) and the second demodulation transfer gate (TGB), respectively. The phase of the first demodulation signal (STGA) is synchronized with the phase of the transmitted light (TL). In one embodiment, the phase difference between the first demodulation signal (STGA) and the second demodulation signal (STGB) is 180 degrees. A distance measurement method using demodulated signals having different phase differences will be described later with reference to FIGS.

[0044] During periods other than the light-focusing period (TINT), for example, during a reset period (TRST) for initializing the distance pixel and a readout period (TRD) for measuring the amount of photocharge collected during the light-focusing period (TINT), the overflow gate voltage (VOG) has a turn-on voltage level (VON) for discharging the photocharge collected by the common photogate (CPG). In this manner, by discharging the charge using the overflow gates (OG1, OG2) during periods other than the light-focusing period (TINT), a global shutter function can be realized.

[0045] In one embodiment, as shown in FIG. 6, the first DC voltage level (VDC) of the photogate voltage (VPG) during the reset interval (TRST) and the readout interval (TRD) is the same as the second DC voltage level (VDC') of the photogate voltage (VPG) during the focusing interval (TINT). The DC voltage level (VDC) is a voltage level between the high voltage level (VH) and the low voltage level (VL) of the demodulation signals (STGA, STGB). In another embodiment, as shown in FIG. 7, the second DC voltage level (VDC') of the photogate voltage (VPG) during the reset interval (TRST) and the readout interval (TRD) can be different from the first DC voltage level (VDC) of the photogate voltage (VPG) during the focusing interval (TINT). The first DC voltage level (VDC) during the focusing interval (TINT) is a voltage level between the high voltage level (VH) and the low voltage level (VL) of the demodulation signals (STGA, STGB). In sections other than the light-collecting section (TINT), the overflow gates (OG1, OG2) are turned on to discharge the collected photocharges. Therefore, the second DC voltage level (VDC') is appropriately set in consideration of the potential distribution on the channel formed in the semiconductor substrate. Although FIG. 7 shows the second DC voltage level (VDC') as being higher than the first DC voltage level (VDC), depending on the embodiment, the second DC voltage level (VDC') may be lower than the first DC voltage level (VDC).

[0046] Figure 8 is a circuit diagram showing a distance pixel having a two-tub structure using individual photogates, and Figure 9 is a timing diagram showing the operation of the distance pixel having the two-tub structure of Figure 8. Since the distance pixel (PX1') of Figure 8 is similar to the distance pixel (PX1) of Figure 4, the same description as in Figures 4 to 7 will be omitted and only the differences will be described.

[0047] As shown in FIG. 8, the distance pixel (PX1') includes a first photogate (PGA) corresponding to the first tub (TA) that replaces the common photogate (CPG) in FIG. 4, and a second photogate (PGB) corresponding to the second tub (TB).

[0048] 8 and 9, during the light concentration interval (TINT), a first demodulation signal (SPGA) and a second demodulation signal (SPGB) having different phases are respectively provided to the first photogate (PGA) and the second photogate (PGB). During the light concentration interval (TINT), a first transfer control signal (STGA) and a second transfer control signal (STGB) having a constant voltage level are respectively provided to the first transfer gate (TGA) and the second transfer gate (TGB).

[0049] In this manner, the distance pixel PX1′ of FIG. 8 is provided with a toggling demodulation signal (SPGA, SPGB) to a plurality of photogates PGA, PGB corresponding to a plurality of tubs. Generally, photogates have a large size to increase the amount of collected photocharges and thus improve sensing sensitivity. Therefore, providing a toggling demodulation signal (SPGA, SPGB) to a photogate having a large area increases power consumption. On the other hand, the distance pixel PX1 of FIG. 4 according to an embodiment of the present invention can reduce power consumption compared to the distance pixel PX1′ of FIG. 8 by providing a constant DC voltage to the common photogate (CPG) and providing a demodulation signal (STGA, STGB) to a demodulation transfer gate (TGA) having a relatively small area.

[0050] On the other hand, in the distance pixel (PX1') of FIG. 8, the number of signal lines for driving the photogates increases in proportion to the number of photogates. The increase in the number of signal lines acts on constraints in the manufacturing process, and such constraints limit the reduction in the size of the distance pixel. On the other hand, the distance pixel (PX1) of FIG. 4 according to an embodiment of the present invention applies a common photogate (CPG), so that one signal line is required to drive the common photogate (CPG) regardless of the number of tabs, thereby easing constraints in the manufacturing process and allowing the size of the distance pixel to be reduced.

[0051] In this way, the range pixel according to an embodiment of the present invention can reduce the power consumption and size of the range pixel and the time-of-flight sensor including the range pixel by applying one common photogate.

[0052] FIG. 10 is a block diagram illustrating a time-of-flight sensor according to an embodiment of the present invention.

[0053] 10, the time-of-flight sensor 100 includes a sensing unit, a control unit 150, and a light source module 200. The sensing unit includes a pixel array 110, an analog-to-digital conversion (ADC) unit 120, a row scanning circuit 130, and a column scanning circuit 140.

[0054] The pixel array 110 includes depth pixels that convert light (TL) transmitted from the light source module 200 into electrical signals. The depth pixels can provide information about the distance of the object (OBJ) from the time-of-flight sensor 100, along with monochrome image information.

[0055] The pixel array 110 further includes color pixels that provide color image information. In this case, the time-of-flight sensor 100 is a three-dimensional color image sensor that simultaneously provides the color image information and the distance information. In one embodiment, infrared (or near-infrared) filters are formed on the distance pixels, and color filters (e.g., red, green, and blue filters) are formed on the color pixels. Depending on the embodiment, the ratio of the number of distance pixels to the number of color pixels can be changed.

[0056] The ADC unit 120 converts analog signals output from the pixel array 110 into digital signals. Depending on the embodiment, the ADC unit 120 may perform a column ADC that converts analog signals in parallel using an analog-to-digital converter connected to each column line, or a single ADC that converts the analog signals sequentially using a single analog-to-digital converter.

[0057] In some embodiments, the ADC unit 120 includes a correlated double sampling (CDS) unit for extracting the useful signal component. In one embodiment, the CDS unit performs analog double sampling to extract the useful signal component based on the difference between an analog reset signal representing the reset component and an analog data signal representing the signal component.

[0058] In another embodiment, the CDS unit converts the analog reset signal and the analog data signal into digital signals, respectively, and then performs digital double sampling to extract the difference between the two digital signals as the effective signal component.

[0059] In another embodiment, the CDS unit may perform dual correlated double sampling, which performs both the analog double sampling and the digital double sampling.

[0060] The row scanning circuit 130 receives control signals from the control unit 150 and controls row addresses and row scanning of the pixel array 110. The row scanning circuit 130 selects a corresponding row line from among the row lines and provides a signal for activating the corresponding row line to the pixel array 110. In one embodiment, the row scanning circuit 130 includes a row decoder for selecting a row line in the pixel array 110 and a row driver for providing a signal for activating the selected row line.

[0061] The column scanning circuit 140 receives a control signal from the control unit 150 and controls the column address and column scanning of the pixel array 110. The column scanning circuit 140 outputs a digital output signal, i.e., sample data (SDATA), output from the ADC unit 120 to a digital signal processing circuit (not shown) or an external host (not shown). For example, the column scanning circuit 140 can sequentially select multiple analog-to-digital converters in the ADC unit 120 by outputting a horizontal scanning control signal to the ADC unit 120.

[0062] In one embodiment, the column scanning circuit 140 includes a column decoder that selects one of a plurality of analog-to-digital converters and a column driver that transmits the output of the selected analog-to-digital converter to a horizontal transfer line, which has a bit width for outputting the digital output signal.

[0063] The control unit 150 controls the ADC unit 120, the row scanning circuit 130, the column scanning circuit 140, and the light source module 200. The control unit 150 supplies control signals such as clock signals and timing control signals required for the operation of the ADC unit 120, the row scanning circuit 130, the column scanning circuit 140, and the light source module 200. In one embodiment, the control unit 150 includes a logic control circuit, a phase-locked loop (PLL) circuit, a timing control circuit, a communication interface circuit, etc.

[0064] The light source module 200 outputs light having a predetermined wavelength (e.g., infrared or near-infrared light). The light source module 200 includes a light source 210 and a lens 220. The light source 210 is controlled by the controller 150 to output light (TL) whose intensity changes periodically.

[0065] For example, the intensity of the light (TL) may be modulated to have a form such as a pulse wave having a series of pulses, a sine wave, a cosine wave, etc. The light source 210 may be embodied as a light emitting diode (LED), a laser diode, etc.

[0066] The operation of the time-of-flight sensor 100 according to the embodiment of the present invention will now be described.

[0067] The control unit 150 controls the light source module 200 to output light (TL) having a periodically changing intensity. The light (TL) emitted from the light source module 200 is reflected by the object (OBJ) and incident on the distance pixel as received light (RL). The distance pixel is activated by the row scanning circuit 130 and outputs an analog signal corresponding to the received light (RL). The ADC unit 120 can convert the analog signal output from the distance pixel into digital data, i.e., sample data (SDATA). The sample data (SDATA) can also be provided to the control unit 150 by the column scanning circuit 140.

[0068] The control unit 150 or an external processor calculates the distance to the object (OBJ), the horizontal position of the object (OBJ), the vertical position of the object (OBJ), and / or the area of ​​the object (OBJ) from the time-of-flight sensor 100 based on the sample data (SDATA). The control unit 150 controls the diffusion angle and irradiation position of the light (TL) emitted from the light source module 200 based on the measured distance, horizontal position, vertical position, and / or area of ​​the object (OBJ). For example, the control unit 150 adjusts the distance between the light source 210 and the lens 220, the relative positions of the light source 210 and the lens 220, the refractive index of the lens 220, the curvature of the lens 220, etc.

[0069] Light (TL) irradiated onto an area corresponding to an object (OBJ) is reflected from the object (OBJ) and re-enters the distance pixel. The distance pixel outputs an analog signal corresponding to the received light (RL), and the ADC unit 120 converts the analog signal output from the distance pixel into digital data, i.e., sample data (SDATA). The sample data (SDATA) is converted into distance information by the control unit 150 or an external processor, and the distance information is provided to a digital signal processing circuit or an external host. In some embodiments, the pixel array 110 includes color pixels, and color image information is provided to the digital signal processing circuit or the host along with the distance information.

[0070] 11 and 12 are diagrams for explaining an example of measurement and calculation of the distance to a subject using a time-of-flight sensor.

[0071] 10 and 11, the light (TL) emitted from the light source module 200 has a periodically varying intensity, for example, the intensity (i.e., the number of photons per unit area) of the emitted light (TL) has a sinusoidal shape.

[0072] The light (TL) emitted from the light source module 200 is reflected by the object (OBJ) and incident on the pixel array 110 as received light (RL). The pixel array 110 periodically samples the received light (RL). Depending on the embodiment, the pixel array 110 samples the received light (RL) at two sampling points with a 180-degree phase difference, four sampling points with a 90-degree phase difference, or more sampling points for each period of the received light (RL) (i.e., the period of the emitted light (TL)). For example, the pixel array 110 extracts samples (A0, A1, A2, A3) of the received light (RL) at 90-degree, 180-degree, 270-degree, and 360-degree phases of the emitted light (TL) for each period. Based on the samples (A0, A1, A2, A3), the phase difference between the transmitted light (TL) and the received light (RL) can be calculated, and the distance to the object can be calculated based on the phase difference.

[0073] The received light (RL) has an offset (B) that is different from the offset of the light (TL) emitted from the light source module 200 due to additional background light, noise, etc. The offset (B) of the received light (RL) is calculated as shown in Equation 1.

[0074]

number

[0075] Here, A0 represents the intensity of the received light (RL) sampled at 90 degrees out of phase with the emitted light (TL), A1 represents the intensity of the received light (RL) sampled at 180 degrees out of phase with the emitted light (TL), A2 represents the intensity of the received light (RL) sampled at 270 degrees out of phase with the emitted light (TL), and A3 represents the intensity of the received light (RL) sampled at 360 degrees out of phase with the emitted light (TL).

[0076] Due to optical loss, the received light (RL) has an amplitude (A) that is smaller than the amplitude of the light (TL) emitted from the light source module 200. The amplitude (A) of the received light (RL) is calculated as in Equation 2.

[0077]

number

[0078] Monochrome image information for the object (OBJ) is provided based on the amplitude (A) of the received light (RL) for each of the range pixels included in the pixel array 110.

[0079] The received light (RL) is delayed relative to the emitted light (TL) by a phase difference (φ) that corresponds to twice the distance from the time-of-flight sensor 100 to the object (OBJ). The phase difference (φ) of the received light (RL) relative to the emitted light (TL) is calculated as follows:

[0080]

number

[0081] The phase difference (φ) of the received light (RL) relative to the emitted light (TL) corresponds to the time-of-flight (ToF) of the light. The distance from the time-of-flight sensor 100 to the object (OBJ) is calculated using the formula "R=c*ToF / 2" (where R represents the distance to the object (OBJ) and c represents the speed of light). The distance from the time-of-flight sensor 100 to the object (OBJ) is also calculated using the phase difference (φ) of the received light (RL) as shown in Formula 4.

[0082]

number

[0083] Here, f represents the modulation frequency, i.e., the frequency of the emitted light (TL) (or the received light (RL)).

[0084] 11 shows an example in which light (TL) modulated to have a sinusoidal wave shape is used, but depending on the embodiment, the time-of-flight sensor 100 can use various forms of modulated light (TL). Also, the time-of-flight sensor 100 can extract distance information in various ways depending on the waveform of the light (TL) intensity, the structure of the distance pixels, etc.

[0085] Figure 12 is a timing diagram of a time-of-flight sensor including a range pixel with a four-tab structure. Figure 12 is used to explain the modulation timing and demodulation timing, i.e., the control timing operation of the demodulation signal, in the time-of-flight sensor, and the operation of the time-of-flight sensor can be changed in various ways.

[0086] As shown in FIG. 12, the transmitted light (TL) output from the light source is output in synchronization with a signal provided by the control unit 150 of FIG. 10. The first to fourth demodulated signals (DEM1 to DEM4) are output in synchronization with the signal provided by the control unit 150. The first to fourth demodulated signals (DEM1 to DEM4) have phase differences of 0, 90, 180, and 270 degrees with respect to the transmitted light (TL), respectively. As a result, using such first to fourth demodulated signals (DEM1 to DEM4), samples (A0, A1, A2, A3) of the received light (RL) can be extracted from the phases of 90, 180, 270, and 360 degrees of the transmitted light (TL), as described with reference to FIG. 11.

[0087] 12 shows a case where the phase of the demodulated signal, i.e., the phase of the first demodulated signal (DEM1), is the same as the phase of the transmitted light (TL). According to an embodiment of the present invention, the first to fourth demodulated signals (DEM1 to DEM4) are respectively provided to first to fourth demodulation transfer gates arranged symmetrically around a common photogate (CPG).

[0088] 11 and 12 are for explaining the principle of distance measurement of the time-of-flight sensor according to the embodiment of the present invention, but the embodiment of the present invention is not limited thereto. The duty ratio of the transmitted light (TL), and the number, phase difference, and duty ratio of the demodulated signals (DEM1 to DEM4) can be changed in various ways.

[0089] FIG. 13 is a circuit diagram showing a range pixel having a four-tab structure according to an embodiment of the present invention, and FIG. 14 is a diagram showing an embodiment of a layout of the range pixel having the four-tab structure of FIG.

[0090] As shown in Figures 13 and 14, the distance pixel (PX2) includes transistors (TMA, TS1, TT1) corresponding to the first tub (TA), transistors (TMB, TS1, TT1) corresponding to the second tub (TB), transistors (TMC, TS2, TT2) corresponding to the third tub (TC), transistors (TMD, TS2, TT2) corresponding to the fourth tub (TD), transistors (TRS1, TRS2, TSF1, TSF2, TSL1, TSL2) corresponding to the readout circuit, and a common photogate (CPG), overflow gates (OG1, OG2), and photodiode (PD) corresponding to the shared circuit.

[0091] Each of the transistors (TMA, TMB, TMC, TMD, TS1, TS2, TT1, TT2, TRS1, and TRS2) includes a gate disposed on a semiconductor substrate, and a source region and a drain region formed on both sides of the gate on the semiconductor substrate. The gates of the transistors (TMA, TMB, TMC, TMD, TS1, TS2, TT1, TT2, TRS1, and TRS2) correspond to a first demodulation transfer gate (TGA), a second demodulation transfer gate (TGB), a third demodulation transfer gate (TGC), a fourth demodulation transfer gate (TGD), storage gates (SG1 and SG2), FD transfer gates (TG1 and TG2), and reset gates (RG1 and RG2), respectively.

[0092] A photogate voltage (VPG) is applied to the common photogate (CPG), an overflow gate voltage (VOG) is applied to the overflow gates (OG1, OG2), storage control signals (SSG1, SSG2) are applied to the storage gates (SG1, SG2), FD transfer control signals (STG1, STG2) are applied to the FD transfer gates (TG1, TG2), reset signals (RG1, RG2) are applied to the reset gates (RG1, RG2), and select signals (SEL1, SEL2) are applied to the gates of the select transistors (TSL1, TSL2). A first demodulation signal (STGA), a second demodulation signal (STGB), a third demodulation signal (STGC), and a fourth demodulation signal (STGD), which have mutually different phases, are applied to the first demodulation transfer gate (TGA), the second demodulation transfer gate (TGB), the third demodulation transfer gate (TGC), and the fourth demodulation transfer gate (TGD), respectively.

[0093] The photogate voltage (VPG), overflow gate voltage (VOG), storage control signals (SSG1, SSG2), FD transfer control signals (STG1, STG2), reset signals (RG1, RG2), selection signals (SEL1, SEL2), and demodulation signals (STGA, STGB, STGC, STGD) are provided from the row scanning circuit 130 under the control of the control unit 150 of FIG. 10.

[0094] The storage gates (SG1, SG2) are one of the charge storage structures and can temporarily store charge before transferring the charge to the floating diffusion regions (FDA, FDB, FDC, FDD) via the demodulation transfer gates (TGA, TGB, TGC, TGCD). In one embodiment, the charge storage structure can be implemented as the storage gates (SG1, SG2) alone. In another embodiment, the charge storage structure can be implemented as a structure in which a storage diode is further formed in the semiconductor substrate below the storage gates (SG1, SG2). In this way, the inclusion of a charge storage structure in the distance pixel (PX2) enables accurate CDS operation and minimizes read noise. Depending on the embodiment, the FD transfer gates (TG1, TG2) and / or the storage gates (SG1, SG2) can be omitted.

[0095] The charges stored in the floating diffusion regions (FDA, FDB, FDC, FDD) are provided as output signals (VOUTA, VOUTB, VOUTC, VOUTD) via transistors (TSF1, TSF2) that act as source follower buffer amplifiers and select transistors (TSL1, TSL2).

[0096] 14, one common photogate (CPG) is arranged in the central region, and the demodulation transfer gates (TGA, TGB, TGC, TGD) and overflow gates (OG1, OG2) have a symmetrical structure with respect to the common photogate (CPG). The demodulation transfer gates (TGA, TGB, TGC, TGD) are arranged symmetrically with respect to each of the first horizontal line (HLX) and the second horizontal line (HLY) that are perpendicular to each other and pass through the center (CP) of the distance pixel (PX2). In other words, the first demodulation transfer gate (TGA) and the third demodulation transfer gate (TGC) are symmetric with respect to the center of the distance pixel (PX2), and the second demodulation transfer gate (TGB) and the fourth demodulation transfer gate (TGD) are symmetric with respect to the center of the distance pixel (PX2). In addition, the overflow gates (OG1, OG2) are arranged symmetrically with respect to the first horizontal line (HLX) and the second horizontal line (HLY), respectively. This symmetrical structure reduces the characteristic deviation between multiple TUBs and improves the sensing accuracy of the distance pixel.

[0097] FIG. 15 is a timing diagram illustrating one embodiment of the operation of a range pixel having the four-tab structure of FIG.

[0098] 13 to 15, during the light concentration interval (TINT), a photogate voltage (VPG) applied to the common photogate (CPG) has a DC voltage level (VDC) for collecting photocharges, and during the light concentration interval (TINT), an overflow gate voltage (VOG) applied to the overflow gates (OG1, OG2) has a turn-off voltage level (VOFF) for blocking the discharge of the photocharges. Also, during the light concentration interval (TINT), a first demodulation signal (STGA), a second demodulation signal (STGB), a third demodulation signal (STGC), and a fourth demodulation signal (STGD), each having a different phase, are applied to the first demodulation transfer gate (TGA), the second demodulation transfer gate (TGB), the third demodulation transfer gate (TGC), and the fourth demodulation transfer gate (TGD), respectively. The phase of the first demodulation signal (STGA) is synchronized with the phase of the transmitted light (TL). In one embodiment, the phase difference between the first demodulated signal (STGA) and the second demodulated signal (STGB) is 90 degrees, the phase difference between the first demodulated signal (STGA) and the third demodulated signal (STGC) is 180 degrees, and the phase difference between the first demodulated signal (STGA) and the fourth demodulated signal (STGD) is 270 degrees. The ranging method using demodulated signals having such different phase differences is similar to the method described with reference to FIGS.

[0099] During periods other than the light-focusing period (TINT), for example, a reset period (TRST) for initializing the distance pixel and a readout period (TRD) for measuring the amount of photocharge collected during the light-focusing period (TINT), the overflow gate voltage (VOG) has a turn-on voltage level (VON) for discharging the photocharge collected by the common photogate (CPG). In this manner, a global shutter function can be realized by discharging charge using the overflow gates (OG1, OG2) during periods other than the light-focusing period (TINT).

[0100] In one embodiment, as shown in FIG. 15, the DC voltage level (VDC) of the photogate voltage (VPG) during the reset interval (TRST) and the readout interval (TRD) is the same as the DC voltage level (VDC) of the photogate voltage (VPG) during the focusing interval (TINT). The DC voltage level (VDC) is a voltage level between the high voltage level (VH) and the low voltage level (VL) of the demodulation signals (STGA, STGB). In another embodiment, as described with reference to FIG. 7, the second DC voltage level (VDC') of the photogate voltage (VPG) during the reset interval (TRST) and the readout interval (TRD) is different from the first DC voltage level (VDC) of the photogate voltage (VPG) during the focusing interval (TINT). The first DC voltage level (VDC) during the focusing interval (TINT) is a voltage level between the high voltage level (VH) and the low voltage level (VL) of the demodulation signals (STGA, STGB). In sections other than the light-collecting section (TINT), the overflow gates (OG1, OG2) are turned on to discharge the collected photocharges, so the second DC voltage level (VDC') is appropriately set taking into account the potential distribution on the channel formed in the semiconductor substrate.

[0101] 16 and 17 are diagrams illustrating embodiments for sharing floating diffusion regions of range pixels according to embodiments of the present invention.

[0102] The distance pixel (PX3) of FIG. 16 is substantially the same as the distance pixel (PX2) having the 4-tab structure described with reference to FIGS. 13 and 14 except for the layout, so a duplicated description will be omitted.

[0103] The distance pixel (PX3) has one common photogate (CPG) arranged in the central region, and the demodulation transfer gates (TGA, TGB, TGC, TGD) and overflow gates (OG1, OG2) have a symmetrical structure with respect to the common photogate (CPG). The demodulation transfer gates (TGA, TGB, TGC, TGD) are arranged symmetrically with respect to a first horizontal line (HLX) and a second horizontal line (HLY) that are perpendicular to each other and pass through the center (CP) of the distance pixel (PX3). In other words, the first demodulation transfer gate (TGA) and the third demodulation transfer gate (TGC) are symmetrical with respect to the center of the distance pixel (PX3), and the second demodulation transfer gate (TGB) and the fourth demodulation transfer gate (TGD) are symmetrical with respect to the center of the distance pixel (PX3). In addition, the overflow gates (OG1, OG2) are arranged symmetrically with respect to the first horizontal line (HLX) and the second horizontal line (HLY), respectively. This symmetrical structure reduces the characteristic deviation between multiple TUBs and improves the sensing accuracy of the distance pixel.

[0104] 16, a first floating diffusion region (FDA) corresponding to a first tub and a second floating diffusion region (FDB) corresponding to a second tub are electrically connected to each other via a conductive path (LN1), and a third floating diffusion region (FDC) corresponding to a third tub and a fourth floating diffusion region (FDD) corresponding to a fourth tub are electrically connected to each other via a conductive path (LN2). The conductive paths (LN1, LN2) include vertical contacts such as conductive lines and vias formed in a conductive layer on a semiconductor substrate.

[0105] In this case, the first demodulation transfer gate (TGA) corresponding to the first tub and the second demodulation transfer gate (TGB) corresponding to the second tub are supplied with the same demodulation signal having a first phase, and the third demodulation transfer gate (TGC) corresponding to the third tub and the fourth demodulation transfer gate (TGD) corresponding to the fourth tub are supplied with the same demodulation signal having a second phase different from the first phase. In this way, by electrically connecting at least two floating diffusion regions among the plurality of floating diffusion regions to each other, the sensing sensitivity of the distance pixel can be increased.

[0106] For convenience of illustration, Figure 17 shows four distance pixels (PXa, PXb, PXc, PXd) adjacent in the first horizontal direction (X) and the second horizontal direction (Y), but the pixel array 110 of Figure 10 may have more distance pixels arranged in the same manner.

[0107] 17, four adjacent distance pixels (PXa, PXb, PXc, PXd) can share one shared floating diffusion region. For example, the tubs adjacent to one floating diffusion region (FDB) corresponding to the second tub and included in each of the four distance pixels (PXa, PXb, PXc, PXd) are all tubs corresponding to demodulated signals of the same phase. In other words, the four second demodulation transfer gates (TGBs) included in each of the four distance pixels (PXa, PXb, PXc, PXd) are provided with second demodulated signals having the same phase, and photocharges corresponding to the second demodulated signals collected by the four distance pixels (PXa, PXb, PXc, PXd) are combined with the central floating diffusion region (FDB). In this manner, the photocharges collected by four adjacent pixels are combined in each of the first shared floating diffusion region (FDA) corresponding to the first tub, the second shared floating diffusion region (FDB) corresponding to the second tub, the third shared floating diffusion region (FDC) corresponding to the third tub, and the fourth shared floating diffusion region (FDD) corresponding to the fourth tub. In this manner, a structure in which multiple distance pixels share a floating diffusion region increases the sensing sensitivity of the distance pixels.

[0108] 18-19 are diagrams illustrating the layout of distance pixels according to an embodiment of the present invention.

[0109] 18a to 18c, the distance pixels (PX4, PX5, PX6) having a four-tub structure include a common photogate (CPG) disposed in the central region, first to fourth demodulation transfer gates (TGA, TGB, TGC, TGD) corresponding to the first to fourth tubs, respectively, and multiple overflow gates (OG). For convenience of illustration, other components are omitted.

[0110] The first to fourth demodulation transfer gates (TGA, TGB, TGC, TGD) are arranged symmetrically with respect to a first horizontal line (HLX) and a second horizontal line (HLY) that are perpendicular to each other through the center (CP) of the distance pixel. Also, a plurality of overflow gates (OG) are arranged symmetrically with respect to the first horizontal line (HLX) and the second horizontal line (HLY). This symmetrical structure reduces characteristic deviations between the plurality of TUBs, thereby improving sensing accuracy of the distance pixel.

[0111] 18a to 18c, the shape of the common photogate (CPG) can be changed in various ways. Depending on the shape of the common photogate (CPG), the first to fourth demodulation transfer gates (TGA, TGB, TGC, TGD) are arranged at appropriate positions so as to have a symmetrical structure, and various numbers of multiple overflow gates (OG) are arranged at appropriate positions so as to have a symmetrical structure.

[0112] 19a to 19c, the distance pixels (PX7, PX8, PX9) having a two-tub structure include a common photogate (CPG) disposed in the central region, first and second demodulation transfer gates (TGA, TGB) corresponding to the first and second tubs, respectively, and multiple overflow gates (OG). For convenience of illustration, other components are omitted.

[0113] The first and second demodulation transfer gates (TGA, TGB) are arranged symmetrically with respect to each of the first horizontal line (HLX) and the second horizontal line (HLY) that are perpendicular to each other through the center (CP) of the distance pixel, or with respect to the center (CP). Also, the plurality of overflow gates (OG) are arranged symmetrically with respect to each of the first horizontal line (HLX) and the second horizontal line (HLY). Such a symmetrical structure can reduce characteristic deviations between the plurality of TUBs and improve sensing accuracy of the distance pixel.

[0114] 19a to 19c, the configuration of the common photogate (CPG) can be changed in various ways, so that the first and second demodulation transfer gates (TGA, TGB) are arranged at appropriate positions to have a symmetrical structure, and various numbers of multiple overflow gates (OG) are arranged at appropriate positions to have a symmetrical structure, depending on the configuration of the common photogate (CPG).

[0115] Fig. 20 is a cross-sectional view showing a distance pixel according to an embodiment of the present invention, and Figs. 21a and 21b are perspective views showing an embodiment of a common photogate included in the distance pixel of Fig. 20. Below, the structure of the common photogate (CPG) will be described, omitting explanations that overlap with those previously described.

[0116] As shown in Figures 20, 21a, and 21b, the distance pixel (PX10) includes a common photogate (CPG) arranged in a central region and multiple demodulation transfer gates (TGA, TGB) arranged symmetrically with respect to the common photogate (CPG).

[0117] The common photogate (CPG) includes a horizontal photogate (PPG) and one or more vertical photogates (ZPG). The horizontal photogate (PPG) is formed in a plate shape parallel to the upper surface of the semiconductor substrate (SUB) and is disposed on the upper part of the semiconductor substrate (SUB). The vertical photogate (ZPG) is connected to the lower surface of the horizontal photogate (PPG) and extends long in the vertical direction (Z) perpendicular to the upper surface of the semiconductor substrate (SUB). The vertical photogate (ZPG) extends to a position close to a photodiode (PD) formed deep in the semiconductor substrate (SUB). The vertical photogate (ZPG) is disposed inside one or more trenches (TRC) formed in the upper region of the semiconductor substrate (SUB). The inside of the trenches (TRC) is filled with a dielectric material.

[0118] In this way, by increasing the surface areas of the semiconductor substrate (SUB) and the common photogate (CPG) and extending the vertical photogate (ZPG) close to the photodiode (PD) formed at a deep position, the collection of photocharges can be promoted. In particular, in the case of a structure having multiple vertical photogates (ZPG) as shown in Fig. 21, the electric field between the trenches (TRC) is strengthened, which can further promote the collection of photocharges.

[0119] FIG. 22 is a cross-sectional view of a range pixel according to an embodiment of the present invention, and FIGS. 23a and 23b are perspective views of an embodiment of a common photogate included in the range pixel of FIG.

[0120] As shown in Figures 22, 23a and 23b, the distance pixel (PX11) includes a common photogate (CPG) arranged in a central region and multiple demodulation transfer gates (TGA, TGB) arranged symmetrically with respect to the common photogate (CPG).

[0121] The common photogate (CPG) extends in a vertical direction perpendicular to the upper surface of the semiconductor substrate (SUB) and includes one or more vertical photogates (ZPG) disposed within one or more trenches (TRC) formed in an upper region of the semiconductor substrate. The distance pixel (PX11) of FIG. 22 is substantially the same as the distance pixel (PX10) of FIG. 20 except that the horizontal photogate (PPG) is omitted, and therefore a redundant description will be omitted.

[0122] When a common photogate (CPG) includes multiple vertical photogates (ZPG) without a horizontal photogate, as in the case of Figure 23b, the multiple vertical photogates (ZPG) are electrically connected to each other through vertical contacts such as conductive lines and vias formed in a conductive layer on top of the semiconductor substrate (SUB).

[0123] 24-27 are diagrams illustrating the layout of distance pixels according to an embodiment of the present invention.

[0124] Figure 24 shows range pixels (PX21 to PX24) having a four-tab structure in which the common photogate includes a horizontal photogate (PPG) and one or more vertical photogates (ZPG). Figure 25 shows range pixels (PX25 to PX28) having a two-tab structure in which the common photogate includes a horizontal photogate (PPG) and one or more vertical photogates (ZPG).

[0125] Figure 26 shows distance pixels (PX31 to PX33) having a four-tab structure in which the common photogate excludes the horizontal photogate (PPG) and includes only one or more vertical photogates (ZPG). Figure 27 shows distance pixels (PX34 to PX36) having a two-tab structure in which the common photogate excludes the horizontal photogate (PPG) and includes only one or more vertical photogates (ZPG).

[0126] 24 to 27, the shape of the common photogate can be changed in various ways. Depending on the shape of the common photogate or the central region where the common photogate is formed, the demodulation transfer gates (TGA, TGB, TGC, TGD) are arranged at appropriate positions to have a symmetrical structure, and various numbers of vertical photogates (ZPG) are arranged at appropriate positions to have a symmetrical structure within the central region.

[0127] Fig. 28 is a cross-sectional view showing a distance pixel according to an embodiment of the present invention, and Fig. 29 is a perspective view showing one embodiment of a common photogate included in the distance pixel of Fig. 28. Below, the structure of the common photogate (CPG) will be described, omitting explanations that overlap with those previously described.

[0128] As shown in Figures 28 and 29, the distance pixel (PX10) includes a common photogate (CPG) arranged in a central region and multiple demodulation transfer gates (TGA, TGB) arranged symmetrically with respect to the common photogate (CPG).

[0129] The common photogate (CPG) is formed in a plate shape parallel to the upper surface of the semiconductor substrate (SUB), and includes a horizontal photogate (PPG) disposed on the upper part of the semiconductor substrate (SUB).

[0130] In one embodiment, the bottom surface of the horizontal photogate (PPG) has a relief structure (CRSTR) for inducing reflection and scattering of incident light. The relief structure (CRSTR) can be used to induce reflection and scattering of incident light, allowing the light to remain further in the semiconductor substrate (SUB), thereby improving sensing sensitivity.

[0131] Figures 30a to 32 are cross-sectional views of distance pixels according to embodiments of the present invention, which illustrate a structure corresponding to backside illumination (BSI), in which light is incident through the bottom surface 12 of a semiconductor substrate (SUB).

[0132] As shown in Figures 30a to 31c, each of the distance pixels (PX51 to PX56) includes a common photogate (CPG) and a plurality of demodulation transfer gates (TGA, TGB) arranged adjacent to the upper surface 11 of the semiconductor substrate (SUB). The common photogate (CPG) and the plurality of demodulation transfer gates (TGA, TGB) have the same configuration as described above, so redundant explanations will be omitted.

[0133] Each of the distance pixels (PX51 to PX56) further includes an anti-reflection film (RFL), a planarization film (PNL), and a microlens (MLN).

[0134] The anti-reflection coating (RFL) is disposed adjacent to the lower surface 12 of the semiconductor substrate (SUB) onto which light is incident. The anti-reflection coating (RFL) re-reflects light scattered or reflected within the semiconductor substrate (SUB) so that the light remains in the semiconductor substrate (SUB), thereby improving sensing sensitivity. For example, the anti-reflection coating (RFL) has a layered structure in which a fixed charge film and an oxide film are stacked, and is formed using a high-dielectric-constant (high-k) insulating thin film by the atomic layer deposition (ALD) method. For example, hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), STO (strontium titanium oxide), etc. can be used.

[0135] The planarization layer (PNL) is disposed adjacent to the lower surface of the anti-reflection layer (RFL). For example, the planarization layer (PNL) is formed of an insulating film such as silicon oxide (SiO), silicon nitride (SiN), or silicon oxynitride (SiON), or an organic material such as a resin.

[0136] The microlens (MLN) is disposed adjacent to the lower surface of the planarization film (PNL). Light collected by the microlens (MLN) is focused onto the photodiode (PD). For example, the microlens (MLN) is formed from a resin-based material such as a styrene-based resin, an acrylic-based resin, a styrene-acrylic copolymer-based resin, or a siloxane-based resin.

[0137] In addition, each of the distance pixels (PX51 to PX56) further includes a pixel separation structure that extends long in a vertical direction (Z) perpendicular to the lower surface 12 of the semiconductor substrate and is formed in the boundary region with the other pixels to block light from the other pixels.

[0138] In one embodiment, as shown in FIG. 30a, a distance pixel (PX51) includes a backside isolation structure (PSSTR1) extending in the vertical direction (Z) from the lower surface 12 of the semiconductor substrate (SUG). A trench (TRC1) is formed to a predetermined depth, and a sidewall (SWL1) is formed inside the trench (TRC1). The sidewall (SWL1) prevents incident light from penetrating into adjacent distance pixels and prevents incident light from penetrating between adjacent pixels. For example, the sidewall (SWL1) is formed of a material similar to an anti-reflective coating (RFL). The inside of the trench (TRC1) is filled with a dielectric material.

[0139] In another embodiment, as shown in Figure 30b, the distance pixel (PX52) includes a front-side isolation structure (PSSTR2) that extends vertically (Z) from the upper surface 11 of the semiconductor substrate (SUG) and includes a trench (TRC2) and a sidewall (SWL2). In another embodiment, as shown in Figure 30c, the distance pixel (PX53) includes a full isolation structure (PSSTR3) that extends vertically (Z) from the upper surface 11 to the lower surface 12 of the semiconductor substrate (SUG) and includes a trench (TRC3) and a sidewall (SWL3).

[0140] Also, as shown in Figures 31a to 31c, the distance pixels (PX54 to PX56) are arranged adjacent to the upper surface of the anti-reflection film (RFL) and further include a concave-convex structure for inducing reflection and scattering of light from within the semiconductor substrate (SUB).

[0141] As shown in Figure 31a, the relief structure (CRSTR1) may include one relief (CR) formed in the trench (TRC), and as shown in Figure 31b, the relief structure (CRSTR2) may include multiple reliefs (CR1, CR2, CR3) having the same length. Depending on the embodiment, as shown in Figure 31c, the relief structure (CRSTR3) may include multiple reliefs (CR1, CR2, CR3) having different lengths.

[0142] 32, the distance pixel (PX61) further includes a polarization structure (PLSTR) disposed adjacent to the lower surface of the anti-reflection film (RFL) for selectively transmitting light having a specific polarization axis. The polarization structure (PLSTR) has a stacked structure of a metal pattern (PTN1) and a dielectric pattern (PTN2).

[0143] 33a and 33b show examples of polarization structures included in the range pixels of FIG.

[0144] As shown in Figure 33a, four distance pixels (PXa, PXb, PXc, PXd) adjacent in the first horizontal direction (X) and the second horizontal direction (Y) each include a polarization structure including a polarization pattern (PLPTN) rotated by 45 degrees. As shown in Figure 33b, among the four adjacent distance pixels (PXa, PXb, PXc, PXd), only some distance pixels (PXa, PXd) include a polarization structure including a polarization pattern (PLPTN), and some distance pixels (PXb, PXc) may not include a polarization pattern (PLPTN).

[0145] FIG. 34 is a block diagram showing an example in which the image sensor of the present invention is applied to a computer system.

[0146] As shown in Fig. 34, the computer system 1000 includes a processor 1010, a memory device 1020, a storage device 1030, an input / output device 1040, a power supply 1050, and a time-of-flight sensor 100. Meanwhile, although not shown in Fig. 34, the computer system 1000 further includes a port for communicating with a video card, a sound card, a memory card, a USB device, or the like, or for communicating with other electronic devices.

[0147] The processor 1010 can perform specific calculations or tasks. In some embodiments, the processor 1010 is a microprocessor, a central processing unit (CPU). The processor 1010 can communicate with memory devices 1020, storage devices 1030, and input / output devices 1040 via an address bus, a control bus, and a data bus.

[0148] In some embodiments, the processor 1010 may also be connected to an expansion bus, such as a Peripheral Component Interconnect (PCI) bus. The memory device 1020 may store data necessary for the operation of the computer system 1000.

[0149] For example, the memory device 1020 can be embodied as DRAM, mobile DRAM, SRAM, PRAM, FRAM, RRAM, and / or MRAM. The storage device 1030 can include a solid-state drive, a hard disk drive, a CD-ROM, etc. The input / output device 1040 can include input means such as a keyboard, a keypad, a mouse, etc., and output means such as a printer, a display, etc. The power supply 1050 provides the operating voltage required for the operation of the electronic device 1000.

[0150] The time-of-flight sensor 100 can be connected to and communicate with the processor 1010 via the bus or other communication link. As previously described, the time-of-flight sensor 100 includes at least one range pixel having a symmetrical structure centered around a common photogate. The time-of-flight sensor 100 can be integrated with the processor 1010 on a single chip or on different chips.

[0151] FIG. 35 is a block diagram illustrating an example of an interface that may be used in the computer system of FIG.

[0152] As shown in FIG. 35, the computer system 1100 may be implemented with a data processing device that can use or support a MIPI interface, and may include an application processor 1110, a time-of-flight sensor 1140, and a display 1150.

[0153] The CSI host 1112 of the application processor 1110 can serially communicate with the CSI unit 1141 of the time-of-flight sensor 1140 via a camera serial interface (CSI).

[0154] In one embodiment, CSI host 1112 includes a deserializer (DES) and CSI device 1141 includes a serializer (SER). DSI host 1111 of application processor 1110 can serially communicate with DSI device 1151 of display 1150 via a display serial interface (DSI).

[0155] In one embodiment, DSI host 1111 includes a serializer (SER) and DSI device 1151 includes a deserializer (DES). Additionally, computer system 1100 further includes a radio frequency (RF) chip 1160 capable of communicating with application processor 1110.

[0156] The PHY 1113 of the computer system 1100 and the PHY 1161 of the RF chip 1160 can transmit and receive data via MIPI (Mobile Industry Processor Interface) DigRF. The application processor 1110 further includes a DigRF master 1114 that controls the data transmission and reception of the PHY 1161 via MIPI DigRF.

[0157] Meanwhile, the computer system 1100 includes a GPS 1120, storage 1170, a microphone 1180, a DRAM 1185, and a speaker 1190. The computer system 1100 can also perform communication using an Ultra Wide Band (UWB) 1210, a Wireless LAN (WLAN) 1220, and a Worldwide Interoperability for Microwave Access (WIMAX) 1230. However, the structure and interface of the computer system 1100 are merely examples and are not intended to be limiting.

[0158] As described above, the range pixel according to the embodiment of the present invention can reduce the power consumption and size of the range pixel and the time-of-flight sensor including the range pixel by applying one common photogate. Furthermore, the range pixel according to the embodiment of the present invention can improve the performance of the range pixel and the time-of-flight sensor including the range pixel by increasing the sensing accuracy and sensing sensitivity through the symmetrical structure and modified structure of the common photogate. [Industrial Applicability]

[0159] Embodiments of the present invention may be usefully applied to devices and systems that include time-of-flight sensors. For example, embodiments of the present invention may be usefully applied to electronic devices such as computers, laptops, mobile phones, smartphones, personal digital assistants (PDAs), portable multimedia players (PMPs), digital TVs, digital cameras, portable game consoles, navigation devices, wearable devices, internet of things (IoT) devices, internet of everything (IoE) devices, e-books, virtual reality (VR) devices, augmented reality (AR) devices, vehicle navigation systems, videophones, surveillance systems, autofocus systems, tracking systems, motion detection systems, etc.

[0160] While the present invention has been described above with reference to preferred embodiments, those skilled in the art will appreciate that various modifications and variations of the present invention may be made without departing from the spirit and scope of the invention as set forth in the following claims.

Claims

1. a common photogate located in a central region of the distance pixel; a plurality of floating diffusion regions disposed in an outer region surrounding the central region; a plurality of demodulation transfer gates arranged in the outer region symmetrically with respect to a first horizontal line and a second horizontal line that pass through the center of the distance pixel and are perpendicular to each other, so as to transfer the photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively; a plurality of overflow gates disposed in the outer region symmetrically with respect to each of the first horizontal line and the second horizontal line to drain the photocharges collected by the common photogate; the common photogate includes at least one vertical photogate extending in a vertical direction perpendicular to an upper surface of the semiconductor substrate; the vertical photogate is disposed in a trench formed in an upper region of the semiconductor substrate, a portion of the vertical photogate being disposed below the upper surface of the semiconductor substrate; a DC voltage level of a photogate voltage during a reset period for initializing the distance pixel and a readout period for measuring an amount of photocharge collected during a light-focusing period is different from a DC voltage level of the photogate voltage during the light-focusing period; A range pixel of a time-of-flight sensor, wherein the DC voltage level of the photogate voltage is constant during the light-concentration period, and the plurality of demodulation transfer gates are each provided with a plurality of demodulation signals having different phases from each other during the light-concentration period.

2. the photogate voltage applied to the common photogate during a light collection interval has a DC voltage level for collecting the photocharges; 2. The distance pixel of the time-of-flight sensor of claim 1, wherein an overflow gate voltage applied to the plurality of overflow gates during the light collection period has a turn-off voltage level for blocking the discharge of the photocharges.

3. 3. The range pixel of the time-of-flight sensor of claim 2, wherein during a reset period for initializing the range pixel and a readout period for measuring the amount of photocharge collected during the light collection period, the overflow gate voltage has a turn-on voltage level for discharging the photocharge collected by the common photogate.

4. The common photogate is 2. The distance pixel of the time-of-flight sensor according to claim 1, further comprising a horizontal photogate formed in a plate shape parallel to an upper surface of a semiconductor substrate and disposed on the semiconductor substrate.

5. the range pixel, wherein the plurality of demodulation transfer gates have a two-tub structure including a first demodulation transfer gate and a second demodulation transfer gate; a first demodulation signal is applied to the first demodulation transfer gate during a light-gathering interval, and a second demodulation signal having a phase difference of 180 degrees with the first demodulation signal is applied to the second demodulation transfer gate; The range pixel of a time-of-flight sensor of claim 1 , wherein the first demodulation transfer gate and the second demodulation transfer gate are symmetrical about a center of the range pixel.

6. the distance pixel has a four-tab structure, the plurality of demodulation transfer gates including a first demodulation transfer gate, a second demodulation transfer gate, a third demodulation transfer gate, and a fourth demodulation transfer gate; During a light-concentration interval, a first demodulated signal is provided to the first demodulation transfer gate, a second demodulated signal having a phase difference of 90 degrees from the first demodulated signal is provided to the second demodulation transfer gate, a third demodulated signal having a phase difference of 180 degrees from the first demodulated signal is provided to the third demodulation transfer gate, and a fourth demodulated signal having a phase difference of 270 degrees from the first demodulated signal is provided to the fourth demodulation transfer gate; 2. The range pixel of a time-of-flight sensor of claim 1, wherein the first demodulation transfer gate and the third demodulation transfer gate are symmetrical about the center of the range pixel, and the second demodulation transfer gate and the fourth demodulation transfer gate are symmetrical about the center of the range pixel.

7. a light source that irradiates a subject with modulated transmitted light; a sensing unit including one or more range pixels that provides distance information from the time-of-flight sensor to the object based on received light reflected from the object; a control unit that controls the light source and the sensing unit, Each of the distance pixels is a common photogate located in a central region of the distance pixel; a plurality of floating diffusion regions disposed in an outer region surrounding the central region; a plurality of demodulation transfer gates arranged in the outer region symmetrically with respect to a first horizontal line and a second horizontal line that pass through the center of the distance pixel and are perpendicular to each other, so as to transfer the photocharges collected by the common photogate to the plurality of floating diffusion regions, respectively; a plurality of overflow gates disposed in the outer region symmetrically with respect to each of the first horizontal line and the second horizontal line so as to drain the photocharges collected by the common photogate; the common photogate includes at least one vertical photogate extending in a vertical direction perpendicular to an upper surface of the semiconductor substrate; the vertical photogate is disposed in a trench formed in an upper region of the semiconductor substrate, a portion of the vertical photogate being disposed below the upper surface of the semiconductor substrate; a DC voltage level of a photogate voltage during a reset period for initializing the distance pixel and a readout period for measuring an amount of photocharge collected during a light-focusing period is different from a DC voltage level of the photogate voltage during the light-focusing period; a DC voltage level of the photogate voltage is constant during the light-focusing interval, and a plurality of demodulation signals having different phases are respectively applied to the plurality of demodulation transfer gates during the light-focusing interval.

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