Solid-State Imaging Pixel Driving Method for Dark Current Suppression
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Solution Overview
Problem
Conventional solid-state imaging apparatuses face issues with dark current mixing into the carrier holding portion and maintaining the withstand voltage of the transfer portion, particularly when operating at low voltages, due to inadequate consideration of voltage amplitudes and relationships between different electrodes during accumulating and non-conducting periods.
Innovation Solution
A driving method for a solid-state imaging apparatus that involves supplying a first voltage to the transfer electrode opposite in polarity during its non-conducting period and a second voltage, of the same polarity but larger in absolute value, to the control electrode of the carrier holding portion during the accumulating period to suppress dark current and maintain the withstand voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the impurity concentration of the semiconductor region of the carrier holding portion is increased to increase the amount of carriers retained, then the carrier holding capability is improved, but dark current generation at the boundary between the semiconductor region and surface oxide film increases
Solution Approach 1:
The patent applies different impurity concentrations to different regions: the photoelectric conversion element has higher impurity concentration for carrier accumulation, while the carrier holding portion has lower impurity concentration to reduce dark current. This local differentiation of material properties resolves the contradiction between carrier retention and dark current suppression.
Solution Approach 2:
The carrier holding portion acts as an intermediary structure with specifically engineered lower impurity concentration that mediates between the photoelectric conversion element and the readout circuitry. This intermediary region prevents dark current generation while maintaining carrier transfer capability.
2Object-generated harmful factors
If a voltage is supplied to the control electrode of the carrier holding portion during the accumulating period, then dark current mixing into the carrier holding portion is suppressed, but the withstand voltage of the transfer portion may be compromised
Solution Approach 1:
The patent applies periodic voltage pulses to the control electrode of the carrier holding portion - applying voltage during the accumulating period to suppress dark current, and removing voltage during the transfer period to maintain withstand voltage. This time-dependent periodic control resolves the contradiction between dark current suppression and voltage reliability.
Solution Approach 2:
The control electrode voltage is dynamically adjusted based on the operational phase: a specific voltage level is applied during the accumulating period for dark current suppression, and the voltage is changed during the transfer period to maintain proper electrical characteristics. This dynamic voltage control resolves the static contradiction.
3Use of energy by moving object
If the solid-state imaging apparatus operates at low voltage, then power consumption is reduced, but maintaining the withstand voltage of the transfer portion becomes more difficult
Solution Approach 1:
The patent changes the voltage parameter dynamically based on operational requirements: during the accumulating period, a voltage is applied to the carrier holding portion control electrode for dark current suppression, while during the transfer period, voltages are coordinated to maintain proper transfer portion withstand voltage. This parameter optimization enables low-voltage operation while maintaining reliability.
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 approach effectively reduces dark current mixing into the carrier holding portion while maintaining the withstand voltage of the transfer portion, enhancing the performance of the solid-state imaging apparatus, especially at low operating voltages.
Implementation Method 1
a photoelectric conversion portion; signal carriers generated in the photoelectric conversion portion
Implementation Method 2
a control electrode arranged above the semiconductor region sandwiching an insulating film between the semiconductor region and the control electrode
Data Source
AI summary
A solid-state imaging apparatus includes the carrier holding portion and the amplifying portion in each pixel, wherein a first voltage supplied to a transfer electrode when the transfer portion for transferring carriers from the carrier holding portion to the amplifying portion is placed in a non-conducting state is opposite in polarity to a voltage supplied to the transfer electrode during the turning on period of the transfer portion, and a second voltage supplied to the control electrode of the carrier holding portion during a holding period in which the carriers are retained in the carrier holding portion is the same in polarity as the first voltage and is larger in absolute value than the first voltage.