Connection Transistor Threshold Voltage Adjustment for Solid-State Imaging
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Solution Overview
Problem
Conventional solid-state imaging devices experience reduced image quality due to leak current generation when the connection transistor is turned off, causing white noise and image degradation.
Innovation Solution
A solid-state imaging device design with a connection transistor that has a higher threshold voltage, narrower channel width, longer channel length, and thicker gate oxide film compared to the reset transistor, along with distinct turn-on and turn-off voltage differences, to effectively manage charge transfer and reduce leak current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the connection transistor is turned off to block charge flow between pixels, then pixel isolation is achieved, but leak current still flows causing image quality degradation
Solution Approach 1:
The patent changes the electrical parameters of the connection transistor by setting its threshold voltage higher than that of the reset transistor. This parameter change enables the connection transistor to block leak current more effectively when turned off, while still allowing sufficient charge transfer when turned on, thus resolving the contradiction between pixel isolation and leak current prevention.
2Ease of operation
If the connection transistor has standard threshold voltage to enable charge transfer, then pixel connectivity is achieved, but leak current flows causing white noise in image
Solution Approach 1:
The patent applies parameter changes by configuring the connection transistor with a higher threshold voltage than the reset transistor. This ensures that when the connection transistor is turned off, it maintains sufficient blocking capability to prevent leak current that would cause white noise, while still allowing effective charge transfer when turned on during normal operation.
3Measurement precision
If the connection transistor threshold voltage is increased to reduce leak current, then image quality improves, but charge transfer efficiency may be reduced
Solution Approach 1:
The patent optimizes the threshold voltage parameter of the connection transistor to be higher than that of the reset transistor but within a range that maintains sufficient charge transfer capability. This balanced parameter setting improves image quality by reducing leak current while preserving adequate charge transfer efficiency for proper pixel operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design improves image quality by minimizing leak current and noise, allowing for better signal readout and expanded dynamic range, even under varying light intensities.
Implementation Method 1
a photoelectric conversion portion that generates and accumulates a charge corresponding to an incident light
Data Source
AI summary
A solid-state imaging device comprises a plurality of pixels that includes a photoelectric conversion portion, a charge-voltage converter that receives the charge and converts the charge to a voltage, an amplifier that outputs a signal corresponding to a potential of the charge-voltage converter, a transfer portion that transfers a charge from the photoelectric conversion portion to the charge-voltage converter, and a reset transistor that resets a potential of the charge-voltage converter; a connection transistor that connects or disconnects the charge-voltage converter of at least one of the pixels and the charge-voltage converter of at least one of the other pixels. A threshold voltage of the connection transistor is higher than a threshold voltage of the reset transistor.