X-ray Detector Pixel Isolation Trenches
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Solution Overview
Problem
Semiconductor X-ray detectors face challenges in accurately measuring X-ray photon energy due to charge sharing, where generated charge carriers are collected by multiple pixels, leading to inaccurate energy measurements, especially in applications requiring high spatial resolution.
Innovation Solution
The implementation of a layer of material or vacuum extending across the thickness of the X-ray absorption layer to encircle each pixel, preventing charge carriers from moving through and thereby limiting charge sharing between pixels, ensuring that each X-ray photon is collected by a single pixel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to achieve high spatial resolution, then spatial resolution is improved, but charge sharing increases leading to inaccurate energy measurement
Solution Approach 1:
The invention introduces isolation structures (such as deep trenches or depleted regions) that segment the semiconductor substrate into distinct pixel regions. These structures physically divide the charge carrier collection paths, preventing charge carriers generated in one pixel from diffusing into adjacent pixels. This segmentation approach allows small pixels to maintain high spatial resolution while avoiding charge sharing through the introduced barriers.
Solution Approach 2:
The invention employs intermediate structures (isolation trenches filled with insulating material or depleted semiconductor regions) that act as mediators between adjacent pixels. These intermediate regions serve as charge carrier barriers that block diffusion paths without affecting the primary detection function of the pixels. The mediators enable close pixel spacing for high resolution while preventing harmful charge sharing.
2Quantity of substance
If pixel size is increased to reduce charge sharing, then charge sharing is reduced, but spatial resolution deteriorates
Solution Approach 1:
By introducing deep isolation structures that extend through most of the semiconductor thickness, the invention creates effective charge carrier barriers that segment the detection volume. This allows the use of smaller pixel dimensions for high spatial resolution while the segmentation structures prevent charge sharing by blocking diffusion paths between pixels.
Solution Approach 2:
The invention applies local quality modification by creating regions with different electrical properties (depleted regions or insulating-filled trenches) at specific locations between pixels. These localized modifications create charge barriers only where needed at pixel boundaries, while the pixel interiors maintain their charge collection properties for high resolution detection.
3Quantity of substance
If isolation structures are added to prevent charge sharing, then charge sharing is reduced, but device complexity increases
Solution Approach 1:
The invention merges the isolation structure fabrication with the existing pixel formation process. The deep trenches or depleted regions are created using the same semiconductor processing steps (photolithography, etching, doping) already required for pixel definition. This integration approach adds minimal process steps while achieving effective charge sharing prevention.
Solution Approach 2:
The isolation structures are formed using self-aligned processes where the pixel definition steps automatically define the isolation region locations. The depleted regions or trench positions are determined by the pixel geometry itself, eliminating the need for separate alignment steps and reducing overall device complexity despite the added functional capability.
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 solution effectively reduces charge sharing, allowing for accurate measurement of X-ray photon energy and maintaining high spatial resolution, even in applications where pixel size is minimized for detailed imaging.
Implementation Method 1
a layer of material or vacuum extending across a thickness of the X-ray absorption layer and encircling the pixel; wherein the layer of material or vacuum is configured to prevent a charge carrier in the pixel from moving through the layer of material
Implementation Method 2
A semiconductor X-ray detector may include a semiconductor layer that absorbs X-ray in wavelengths of interest. When an X-ray photon is absorbed in the semiconductor layer, multiple charge carriers (e.g., electrons and holes) are generated.
Data Source
AI summary
A method of making an apparatus suitable for detecting X-ray is disclosed. In an example, the method includes: obtaining a semiconductor substrate with a first electrical contact on a first surface and a second electrical contact on a second surface opposite the first surface, the second electrical contact comprising a plurality of discrete portions; forming a plurality of trenches extending into at least 70% of a thickness of the semiconductor substrate, wherein the plurality of trenches encircle each of the discrete portions.