Image Sensor Pixel With Lateral Electric Field Charge Transport
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Solution Overview
Problem
Existing solid-state photosensors face challenges in achieving large pixel areas with high quantum efficiency, high photocharge detection sensitivity, and fast response speed while minimizing static current consumption, especially in applications like X-ray and gamma-ray imaging.
Innovation Solution
The solution involves geometrically and electrically separating the tasks of charge conversion, separation, and storage using distinct semiconductor structures, with an array of photogates or implants creating a lateral electric field for charge transport and a floating diffusion for accumulation, allowing for pseudo-static or dynamic operation without clocking circuitry and low power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pixel area is increased to improve quantum efficiency and sensitivity, then the photocharge detection sensitivity decreases due to increased pixel capacitance
Solution Approach 1:
The pixel is divided into two distinct regions: a large photosensitive area for charge generation and a separate small charge storage area (floating diffusion) for charge accumulation and readout. This segmentation allows the photosensitive area to be large for high quantum efficiency while the storage area remains small for low capacitance and high sensitivity.
Solution Approach 2:
A floating diffusion region acts as an intermediary between the large photosensitive area and the readout circuitry. It accumulates photogenerated charges from the large area while maintaining low capacitance, enabling high sensitivity readout without being directly coupled to the large photosensitive area.
2Area of moving object
If conventional photosensor designs are used, then large pixel areas can be achieved, but high response speed and low power consumption cannot be simultaneously obtained
Solution Approach 1:
The floating potential of the diffusion region is dynamically controlled through external electrodes that apply time-varying voltages. This dynamic control enables fast charge collection and rapid reset of the floating diffusion, achieving high response speeds without requiring large pixel areas or complex clocking circuitry.
Solution Approach 2:
The invention replaces the mechanical clocking system of CCDs with an electric field-based charge transport mechanism. External electrodes create electric fields that actively transport charges to the floating diffusion, eliminating the need for sequential clocking and enabling faster response times.
3Area of stationary object
If transimpedance circuit designs are used, then large area detection is achieved, but device complexity and power consumption increase
Solution Approach 1:
The complex transimpedance circuitry is extracted and removed from the pixel structure itself. Only simple charge accumulation on a floating diffusion is performed within the pixel, while signal conversion and amplification are deferred to external readout circuits, significantly reducing in-pixel complexity.
Solution Approach 2:
The floating diffusion region self-regulates its potential through capacitive coupling with the substrate and external electrodes, eliminating the need for complex biasing circuits or active feedback mechanisms within each pixel. The structure automatically maintains the conditions needed for charge accumulation.
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 enables large-area, high-sensitivity, and high-speed photosensors with reduced power consumption, suitable for one-dimensional or two-dimensional arrays, and capable of three-dimensional imaging in real time, using standard CMOS processes and compatible with commercially available semiconductor technologies.
Implementation Method 1
an active area for converting incident radiation into charge carriers of a first and a second charge type
Implementation Method 2
charge-separation means located in said active area for separating said charge carriers of the first charge type from said charge carriers of the second charge type
Data Source
AI summary
The pixel for use in an image sensor comprises a low-doped semiconductor substrate (A). On the substrate (A), an arrangement of a plurality of floating areas e.g., floating gates (FG2-FG6), is provided. Neighboring floating gates are electrically isolated from each other yet capacitively coupled to each other. By applying a voltage (V2-V1) to two contact areas (FG1, FG7), a lateral steplike electric field is generated. Photogenerated charge carriers move along the electric-field lines to the point of highest potential energy, where a floating diffusion (D) accumulate the photocharges. The charges accumulated in the various pixels are sequentially read out with a suitable circuit known from image-sensor literature, such as a source follower or a charge amplifier with row and column select mechanisms. The pixel of offers at the same time a large sensing area, a high photocharge-detection sensitivity and a high response speed without any static current consumption.