Variable Floating Diffusion Structure for Wide-Dynamic-Range Image Sensors
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Solution Overview
Problem
Current CCD image sensors face challenges in achieving high dynamic range and sensitivity due to fixed pn-junction capacitance, limiting their ability to detect both small and large optical signals effectively in semiconductor inspection applications.
Innovation Solution
The implementation of a Voltage-Controlled Variable Floating Diffusion (VCVFD) structure, which allows for adjustable capacitance by controlling the voltage applied to a second gate electrode, enabling a wider range of capacitance values and improving the dynamic range of CCD image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a smaller floating diffusion capacitance is used, then the sensitivity to low-level optical signals is improved, but the maximum detectable signal is reduced
Solution Approach 1:
The patent implements a dynamic capacitance adjustment mechanism where the floating diffusion capacitance can be varied in real-time based on signal conditions. The system switches between different capacitance values (e.g., first capacitance value for low-level signals, second capacitance value for high-level signals) to optimize performance across different operating conditions, resolving the contradiction between sensitivity and maximum detectable signal.
Solution Approach 2:
The patent changes the capacitance parameter of the floating diffusion region from a fixed value to a variable value that can be adjusted according to the optical signal level. By controlling the capacitance parameter dynamically, the system achieves high sensitivity for weak signals while maintaining the ability to detect strong signals, thus resolving the technical contradiction.
2Quantity of substance
If a larger floating diffusion capacitance is used, then the maximum detectable signal is increased, but the sensitivity to low-level optical signals is reduced
Solution Approach 1:
The system dynamically adjusts the floating diffusion capacitance based on the detected signal level. When high-level signals are detected, the system switches to a larger capacitance value to accommodate the maximum signal range. When low-level signals are detected, it switches to a smaller capacitance value to maintain sensitivity, thus resolving the contradiction between maximum detectable signal and sensitivity.
Solution Approach 2:
The patent implements variable capacitance control where the capacitance parameter of the floating diffusion region is changed according to the optical signal conditions. This allows the system to optimize the capacitance parameter for different signal levels, achieving both high maximum detectable signal and high sensitivity as needed.
3Device complexity
If a fixed pn-junction capacitance is used, then the device structure is simple, but the dynamic range is limited
Solution Approach 1:
The patent transforms the fixed capacitance structure into a dynamic structure where the capacitance value can be adjusted. By incorporating control mechanisms that allow real-time capacitance adjustment, the system maintains structural simplicity while achieving extended dynamic range through variable capacitance operation.
Solution Approach 2:
The patent creates a multi-functional floating diffusion structure that can operate in different capacitance modes to handle different signal conditions. This universal structure can adapt to various optical signal levels and inspection requirements, extending the dynamic range while maintaining a relatively simple overall device architecture.
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
The VCVFD structure enhances the dynamic range of CCD image sensors, allowing for improved detection of both low-level and high-level optical signals, thereby increasing sensitivity and inspection capabilities in semiconductor applications.
Implementation Method 1
a silicon layer configured to generate electron-hole pairs when light is incident on a light-sensitive area of the silicon layer
Implementation Method 2
The capacitance of the image sensor FD region defines the upper and lower limits of detectable optical signals
Data Source
AI summary
Image sensors with a tunable floating diffusion (FD) structure for applications such as inspection and metrology are provided. One image sensor includes a sensing node electrically connected to circuits of the image sensor, formed on a first side of a silicon layer adjacent to the circuits, and formed by a Voltage-Controlled Variable Floating Diffusion (VCVFD) structure. The VCVFD structure includes a gate electrode configured to control a variable capacitance of the VCVFD structure via voltage applied to the gate electrode by an electrical connection to the gate electrode. The VCVFD structure converts a charge responsive to electron accumulation in the channel of the circuits to a voltage proportional to an amount of the charge and dependent on the variable capacitance. The VCVFD may also be implemented in an electron-sensor pixel configured for detecting electrons or x-rays as described further herein.