Solid-state imaging device, method of driving the same, and electronic apparatus
The present technology relates to a solid-state imaging device that can improve imaging quality by reducing variation in the voltage of a charge retention unit, a method of driving the solid-state imaging device, and an electronic apparatus. A first photoelectric conversion unit generates and accumulates signal charge by receiving light that has entered a pixel, and photoelectrically converting the light. A first charge retention unit retains the generated signal charge. A first output transistor outputs the signal charge in the first charge retention unit as a pixel signal, when the pixel is selected by the first select transistor. A first voltage control transistor controls the voltage of the output end of the first output transistor. The present technology can be applied to pixels in solid-state imaging devices, for example.
1. A solid-state imaging device comprising
a pixel including:
a first photoelectric conversion unit configured to generate and accumulate signal charge by receiving light and photoelectrically converting the light;
a first floating diffusion configured to retain the signal charge generated by the first photoelectric conversion unit;
a first select transistor configured to control selecting of the pixel;
a first output transistor configured to output the signal charge in the first floating diffusion as a pixel signal when the pixel is selected by the first select transistor; and
a first voltage control transistor configured to control a voltage of an output of the first output transistor; and
a drive circuit configured to control the first voltage control transistor to be invariably in an off-state while the first select transistor is in an on-state.
2. The solid-state imaging device according to claim 1 , wherein:
the first photoelectric conversion unit photoelectrically converts light of a first wavelength; and
the pixel further includes:
a second photoelectric conversion unit configured to generate signal charge by receiving light of a second wavelength and photoelectrically converting the light, the second wavelength being different from the first wavelength;
a third photoelectric conversion unit configured to generate signal charge by receiving light of a third wavelength and photoelectrically converting the light, the third wavelength being different from the first wavelength and the second wavelength;
a second floating diffusion configured to retain the signal charge generated by the second and third photoelectric conversion units;
a second select transistor configured to control selecting of the pixel; and
a second output transistor configured to output the signal charge in the second floating diffusion as a pixel signal when the pixel is selected by the second select transistor.
3. The solid-state imaging device according to claim 2 , wherein the pixel further includes
a second voltage control transistor configured to control a voltage of an output end of the second output transistor.
4. The solid-state imaging device according to claim 1 , wherein the first photoelectric conversion unit is formed with a structure having a photoelectric conversion film interposed between upper and lower electrodes.
5. The solid-state imaging device according to claim 1 , wherein the first photoelectric conversion unit is formed with a photodiode formed by a PN junction in a semiconductor substrate, and wherein the first voltage control transistor is coupled to a node between the first output transistor and the first select transistor.
6. The solid-state imaging device according to claim 1 , wherein the signal charge generated by the first photoelectric conversion unit is holes.
7. The solid-state imaging device according to claim 1 , wherein the signal charge generated by the first photoelectric conversion unit is electrons.
8. The solid-state imaging device according to claim 1 , wherein:
the first floating diffusion includes a diffusion layer of a second conductivity type, the diffusion layer being formed in a semiconductor substrate of a first conductivity type; and
a reset voltage for resetting a voltage of the first floating diffusion is a voltage equal to a potential of the first conductivity type.
9. The solid-state imaging device according to claim 8 , wherein the first conductivity type is p-type, and the second conductivity type is n-type.
10. The solid-state imaging device according to claim 1 , further comprising
a transfer transistor configured to transfer the signal charge generated by the first photoelectric conversion unit to the first floating diffusion.
11. The solid-state imaging device according to claim 1 , wherein a drain voltage of the first voltage control transistor is equal to a drain voltage of the output transistor.
12. The solid-state imaging device according to claim 1 , wherein the first voltage control transistor is a deep-depletion transistor.
13. The solid-state imaging device according to claim 1 , wherein the drive circuit is configured to apply a negative bias as an off-state voltage of the first voltage control transistor.
14. The solid-state imaging device according to claim 1 , wherein the drive circuit is configured to switch off the first voltage control before the first select transistor is switched on.
15. The solid-state imaging device according to claim 1 , wherein the drive circuit is configured to reset the first floating diffusion while the first select transistor is in an on-state and the first voltage control transistor is in an off-state before signal accumulation is performed by the first photoelectric conversion unit while the drive circuit controls the first select transistor to be in an off-state and the first voltage control transistor to be in an on-state.
16. The solid-state imaging device according to claim 1 , wherein the drive circuit is configured to reset the first floating diffusion while the first select transistor is in an off-state and the first voltage control transistor is in an on-state, and readout a signal at the time of the reset while the drive circuit controls the first select transistor to be in an on-state and the first voltage control transistor to be in an off-state.
17. A method of driving a solid-state imaging device including a drive circuit and a pixel, the pixel including a first photoelectric conversion unit, a first floating diffusion, a first select transistor, a first output transistor, and a first voltage control transistor, the method comprising:
the first photoelectric conversion unit generating and accumulating signal charge by receiving light and photoelectrically converting the light;
the first floating diffusion retaining the signal charge generated by the first photoelectric conversion unit;
the first select transistor controlling selecting of the pixel;
the first output transistor outputting the signal charge in the first floating diffusion as a pixel signal when the pixel is selected by the first select transistor;
the first voltage control transistor controlling a voltage of an output of the first output transistor,
the drive circuit controlling the first voltage control transistor to be invariably in an off-state while the first select transistor is in an on-state.
18. An electronic apparatus comprising
a solid-state imaging device including a pixel, the pixel including:
a first photoelectric conversion unit configured to generate and accumulate signal charge by receiving light having entered the pixel and photoelectrically converting the light;
a first floating diffusion configured to retain the signal charge generated by the first photoelectric conversion unit;
a first select transistor configured to control selecting of the pixel;
a first output transistor configured to output the signal charge in the first floating diffusion as a pixel signal when the pixel is selected by the first select transistor; and
a first voltage control transistor configured to control a voltage of an output of the first output transistor; and
a drive circuit configured to control the first voltage control transistor to be invariably in an off-state while the first select transistor is in an on-state.