Buried-Junction LGAD Readout Structure for Fine Granularity
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Solution Overview
Problem
Conventional Low-Gain Avalanche Detectors (LGADs) face limitations in granularity due to high electric fields causing breakdown in the readout structure, resulting in a dead region that hampers spatial resolution below 1 mm, which is insufficient for applications like particle physics and high-frame-rate X-Ray imaging.
Innovation Solution
The implementation of a buried junction in avalanche diodes localizes the high electric field region away from the readout structure, eliminating the need for Junction Termination Extension (JTE) and allowing for higher granularity by maintaining a low electric field near the surface, thereby enhancing spatial resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high electric field is applied to generate avalanche gain, then internal gain is improved, but breakdown occurs in the readout structure limiting granularity
Solution Approach 1:
The device is segmented into distinct functional regions: a gain region with high electric field for avalanche multiplication and a readout region with low electric field for signal collection. The gain region is further divided into multiple gain layers stacked vertically, allowing independent optimization of gain and readout regions. This segmentation enables simultaneous achievement of high internal gain and fine granularity in the readout structure.
Solution Approach 2:
Different regions of the device are assigned different electric field characteristics tailored to their specific functions. The gain region maintains high electric field strength (on the order of 10^5 V/cm) to enable avalanche multiplication, while the readout region maintains low electric field strength to prevent breakdown and allow fine segmentation. This local differentiation of electric field quality resolves the contradiction between gain and granularity.
2Reliability
If Junction Termination Extension (JTE) is used to prevent breakdown, then reliability is improved, but dead region increases reducing spatial resolution
Solution Approach 1:
The harmful high electric field is extracted and confined to the gain region, separating it from the readout region. By confining the high field to specific gain layers and using low-field separation regions between them, the patent eliminates the need for JTE structures in the readout region. This extraction of the high field from the readout area prevents breakdown while eliminating dead regions, thereby maintaining both reliability and fine spatial resolution.
Solution Approach 2:
Low electric field separation regions act as intermediaries between the high-field gain regions and the readout structure. These intermediate regions provide electrostatic isolation and prevent breakdown propagation while maintaining continuity of the device structure. This intermediary approach eliminates the need for JTE and removes dead regions that would otherwise be required for breakdown prevention.
3Manufacturing precision
If fine granularity is achieved, then spatial resolution is improved, but breakdown occurs at higher granularity limits
Solution Approach 1:
The gain region is segmented into multiple stacked gain layers separated by low-field regions. This vertical segmentation allows the readout structure to be finely segmented for high spatial resolution while the gain layers maintain the necessary high electric fields for avalanche multiplication. The segmentation prevents breakdown by isolating high-field regions from each other and from the readout structure.
Solution Approach 2:
The patent applies different electric field qualities to different spatial locations: high electric field in the gain layers for multiplication and low electric field in the readout region for fine-grained signal collection. This local differentiation allows the readout structure to achieve fine granularity (50 μm or less) without experiencing breakdown, as the low field quality in the readout region prevents avalanche multiplication while maintaining signal collection 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 approach significantly improves the granularity of LGADs, enabling applications at the 50 μm scale without the dead region, maintaining internal gain, timing resolution, and achieving a repetition rate in excess of 1 GHz.
Implementation Method 1
the p-n junction generates an avalanche of additional signal charge through impact ionization in response to a reverse bias electric field
Data Source
AI summary
An avalanche diode including a gain region and a readout structure including an n-type (p-type) region having electrically isolated segments each including implanted regions; a p-type (n-type) region; and a first electrode on each of the segments. The gain region includes a p-n junction buried between the n-type region and the p-type region: an n+-type region having a higher n-type dopant density than the n-type region; a p+-type region having a higher p-type dopant density than the p-type region; and the p-n junction between the n+-type region and the p+-type region. A bias between the first electrodes and a second electrode (ohmically contacting the p-type (n-type) region) reverse biases the p-n junction. Electrons generated in response to electromagnetic radiation or charged particles generate additional electrons m the gain region through impact ionization but the segmented region comprises a low field region isolating the gain region from the first electrodes.