Solid-state image pickup device with level shift unit for dark current suppression
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Solution Overview
Problem
Existing solid-state image pickup devices face challenges in suppressing dark current from transfer transistors and achieving low power-supply voltage, as they do not effectively manage the amplitude of pulses for transfer transistors and have complex structures due to different conductivity types on single semiconductor substrates.
Innovation Solution
A solid-state image pickup device configuration where a pixel array with a photoelectric conversion unit and transfer transistor is on a first semiconductor substrate, and common output lines and signal processing units are on a second substrate, incorporating a level shift unit to increase the pulse amplitude for transfer transistors, and using PMOS transistors for amplification and reset operations to manage voltage ranges and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the gate insulating film of the transfer transistor is thinned to reduce leakage current, then dark current suppression is improved, but the transistor becomes more sensitive to voltage fluctuations and harder to control
Solution Approach 1:
The patent applies different gate insulating film thicknesses to different transistor types: the transfer transistor has a thinner gate insulating film (first thickness) to reduce leakage current and dark current, while other transistors have a thicker gate insulating film (second thickness) for stable voltage control. This local differentiation resolves the contradiction by optimizing each transistor type for its specific function rather than using a uniform thickness.
Solution Approach 2:
The patent changes the physical parameter of gate insulating film thickness specifically for the transfer transistor to achieve lower leakage current. By modifying this parameter locally for the transfer transistor while maintaining standard thickness for other transistors, the patent suppresses dark current without compromising the voltage control stability of other circuit components.
2Object-generated harmful factors
If the pulse amplitude for the transfer transistor is increased to prevent dark current, then dark current suppression is improved, but the power supply voltage requirement increases
Solution Approach 1:
The patent provides different voltage ranges locally for different transistor types: the transfer transistor receives a wider voltage range (including higher amplitudes) to suppress dark current, while other transistors operate with a narrower, lower voltage range to reduce power consumption. This local voltage differentiation allows dark current suppression without increasing the overall power supply voltage requirement.
Solution Approach 2:
The patent dynamically adjusts the voltage amplitude delivered to different transistor types based on their functional requirements. The transfer transistor receives higher amplitude pulses when needed for charge transfer to prevent dark current, while other transistors receive lower amplitude signals for normal operation, thereby suppressing dark current without maintaining high power supply voltage throughout the entire circuit.
3Device complexity
If all transistors are arranged on a single semiconductor substrate, then device complexity is reduced, but it becomes difficult to optimize different transistor types for different functions
Solution Approach 1:
The patent segments the transistor optimization strategy by transistor type and location: transfer transistors on the first substrate receive specialized treatment (thinner gate insulating film, wider voltage range) while other transistors on the second substrate use standard configurations. This segmentation allows each transistor type to be optimized for its specific function while maintaining overall device manageability through systematic differentiation.
Data Source
AI summary
Dark current from a transfer transistor is suppressed and power-supply voltage in a second semiconductor substrate is lowered. A solid-state image pickup device includes a pixel array, a plurality of common output lines receiving signals read out from a plurality of pixels, a transfer scanning unit sequentially driving the plurality of transfer transistors, a signal processing unit processing the signals output to the common signal lines, and a level shift unit making amplitude of a pulse supplied to a gate of the transfer transistor larger than amplitude of a pulse supplied to a gate of a transistor constituting the signal processing unit. The pixel array and the level shift unit are arranged on a first semiconductor substrate, whereas the plurality of common output lines and the signal processing unit are arranged on a second semiconductor substrate.