Solid-state imaging device and method of driving the same where three levels of potentials including a negative potential are applied in the transfer gate
View Patent ↗A row scanning unit is configured to change a potential of a transfer signal from a second potential V 2 to a third potential V 3 prior to driving of a transfer operation for causing a transfer of signal charges from a photodiode to a floating diffusion, by supplying a transfer pulse having a first potential V 1 . The first potential V 1 is a positive potential for turning a transfer transistor into ON state, the second potential V 2 is a potential for causing pinning of holes under a gate of the transfer transistor and turning the transfer transistor into OFF state, and the third potential V 3 is a potential for not causing the pinning of the holes under the gate of the transfer transistor and turning the transfer transistor into OFF state, the third potential being lower than the first potential and higher than the second potential.
1. A solid-state imaging device comprising:
a plurality of unit cells arranged in rows and columns; and
a row scanning unit configured to generate a reset signal and a transfer signal for driving row scanning of the plurality of unit cells, wherein:
each of the plurality of unit cells includes:
a photodiode which converts incident light into signal charges;
a floating diffusion which holds the signal charges;
a transfer transistor which transfers the signal charges from the photodiode to the floating diffusion according to the transfer signal;
a reset transistor which resets a potential of the floating diffusion according to the reset signal; and
an amplifying transistor which converts the signal charges accumulated in the floating diffusion into voltage,
each of the plurality of unit cells has a read-out state, an unselected state and a shuttered state,
the row scanning unit is configured to, in the read-out state, perform a transfer operation for causing a transfer of the signal charges from the photodiode to the floating diffusion, by supplying a transfer pulse having a first potential,
the row scanning unit is further configured to change a potential of the transfer signal from a second potential to a third potential prior to the transfer operation and then change the potential of the transfer signal from the third potential to the first potential for the transfer operation,
the first potential is a positive potential for turning the transfer transistor into an ON state,
the second potential is a potential for causing pinning of holes under a gate of the transfer transistor and turning the transfer transistor into an OFF state, and
the third potential is a potential for not causing the pinning of the holes under the gate of the transfer transistor and turning the transfer transistor into an OFF state, the third potential being lower than the first potential and higher than the second potential.
2. The solid-state imaging device according to claim 1 ,
wherein the second potential is a negative potential and the third potential is a ground potential.
3. The solid-state imaging device according to claim 1 ,
wherein each of the plurality of unit cells is connected to the amplifying transistor and includes a selection transistor which selects whether or not to output the voltage converted by the amplifying transistor to a column signal line.
4. The solid-state imaging device according to claim 1 ,
wherein the third potential is equal to a potential of a well area in which the transfer transistor is formed.
5. The solid-state imaging device according to claim 1 ,
wherein the row scanning unit is configured to change, in the read-out state, the potential of the transfer signal from the second potential to the third potential prior to a reset operation to reset the potential of the floating diffusion according to the reset signal.
6. The solid-state imaging device according to claim 5 ,
wherein the row scanning unit is configured to change, in the read-out state, the potential of the transfer signal from the second potential to the third potential a predetermined time prior to a start of the reset operation, and
the predetermined time is longer than a time constant indicating a time required to emit the holes from traps under the gate of the transfer transistor.
7. The solid-state imaging device according to claim 1 , further comprising
a sample and hold unit configured to perform a sample and hold operation for sampling and holding, for every column of the plurality of unit cells, the voltage outputted from the amplifying transistor,
wherein the row scanning unit is configured to hold the third potential from the completion of the transfer operation to a completion of the sample and hold operation, and to change the potential of the transfer signal from the third potential to the second potential after the completion of the sample and hold operation.
8. The solid-state imaging device according to claim 1 , further comprising
an AD conversion unit configured to perform analog-to-digital (AD) conversion, for every column of the plurality of unit cells, on the voltage outputted from the amplifying transistor,
wherein the row scanning unit is configured to hold the third potential from the completion of the transfer operation to a completion of the AD conversion, and to change the potential of the transfer signal from the third potential to the second potential after the completion of the AD conversion.
9. A method of driving a solid-state imaging device which includes:
a plurality of unit cells arranged in rows and columns; and a row scanning unit which generates a reset signal and a transfer signal for driving row scanning of the plurality of unit cells,
wherein each of the plurality of unit cells includes:
a photodiode which converts incident light into signal charges;
a floating diffusion which holds the signal charges;
a transfer transistor which transfers the signal charges from the photodiode to the floating diffusion according to the transfer signal;
a reset transistor which resets a potential of the floating diffusion according to the reset signal; and
an amplifying transistor which converts the signal charges accumulated in the floating diffusion into voltage, and
each of the plurality of unit cells has a read-out state, an unselected state and a shuttered state,
the method comprising:
in the read-out state, changing a potential of the transfer signal from a second potential to a third potential in the row scanning prior to a transfer operation; and
in the read-out state, changing the potential of the transfer signal from the third potential to a first potential for the transfer operation for causing a transfer of the signal charges from the photodiode to the floating diffusion in the row scanning,
wherein the first potential is a positive potential for turning the transfer transistor into an ON state,
the second potential is a potential for causing pinning of holes under the gate of the transfer transistor and turning the transfer transistor into an OFF state, and
the third potential is a potential for not causing the pinning of the holes under the gate of the transfer transistor and turning the transfer transistor into an OFF state, the third potential being lower than the first potential and higher than the second potential.
10. A camera comprising the solid-state imaging device according to claim 1 .
11. The solid-state imaging device according to claim 1 , wherein the row scanning unit is configured to supply the second potential during the read-out state except for a period until an import of a signal level has completed after a completion of the transfer operation, the unselected state, and the shuttered state except for a period for resetting the signal charges.
12. The method of claim 9 , wherein the method further comprises supplying the second potential during the read-out state except for a period until an import of a signal level has completed after a completion of the transfer operation, the unselected state, and the shuttered state except for a period for resetting the signal charges.