MISIM Detector Element for Radiography Imaging

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Solution Overview

Problem

Existing radiography imaging systems face challenges with high fabrication costs and performance limitations due to issues with vertical photodiodes and lateral MSM photoconductors, including low yield, high dark currents, non-uniformity, and low effective quantum efficiency.

Innovation Solution

A Metal-Insulator-Semiconductor-Insulator-Metal (MISIM) detector element integrated with a readout circuit element through a dielectric layer, which reduces dark currents and enhances collection efficiency under high electric fields, while being simpler and more cost-effective to manufacture than traditional photodiode structures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a vertical photodiode structure is used, then detection capability is improved, but fabrication complexity and cost increase due to thick amorphous silicon layers, specialized doped contact layers, and complex RIE sidewall etching processes

Engineering Contradiction:

Improvedetection capabilityVSAvoidfabrication complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent inverts the conventional vertical photodiode structure by using a lateral MSM photoconductor configuration where electrodes are arranged horizontally rather than vertically. This inversion simplifies the fabrication process by eliminating the need for thick amorphous silicon layers, specialized doped contact layers, and complex RIE sidewall etching processes, while still achieving effective radiation detection through the photoconductive material

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent changes the structural parameters from a vertical configuration to a lateral configuration, transforming the spatial arrangement of electrodes and photoconductive material. This parameter change enables the same detection function to be achieved with simpler fabrication processes and different material layer requirements

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If a lateral MSM photoconductor is used, then fabrication is simplified, but dark current increases and effective quantum efficiency decreases due to non-uniform electric field and low space efficiency

Engineering Contradiction:

Improvefabrication simplicityVSAvoiddark current performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by creating a non-uniform electrode configuration where the electrode spacing and dimensions are varied locally to achieve a more uniform electric field distribution across the active area. This local optimization of electrode geometry compensates for the inherent non-uniformity in lateral MSM structures, reducing dark current and improving detection uniformity

Inventive Principle:

Principle #3Local quality

3Speed

If higher electric field is applied to lateral MSM photoconductor, then detection speed is improved, but dark current increases significantly

Engineering Contradiction:

Improvedetection speedVSAvoiddark current

Core Design Contradiction:

SpeedVSObject-generated harmful factors

Solution Approach 1:

The patent changes the electric field distribution parameters by optimizing electrode spacing and applying controlled bias voltages to achieve sufficient detection speed while limiting the maximum electric field strength to prevent excessive dark current generation. This parameter optimization balances speed and dark current performance

Inventive Principle:

Principle #35Parameter changes

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 MISIM detector element operates at faster speeds, increases effective quantum efficiency, and provides higher performance with improved reliability and cost-effectiveness, overcoming the limitations of traditional photodetectors in radiography imaging.

Implementation Method 1

a semiconducting layer to absorb incident photons

Methodology Applied

Scientific EffectPhoton absorption: Absorption (EM radiation)

Implementation Method 2

at least one of the electrodes is electrically isolated from the semiconducting layer using an insulator. The insulated contact, also typically under high voltage bias, maintains a low dark current even under high electric field conditions

Methodology Applied

Scientific EffectElectrical insulation: Electrical Resistance

Implementation Method 3

a lateral Metal-Insulator-Semiconductor-Insulator-Metal (or MISIM) detector element... a semiconducting layer to absorb incident photons

Methodology Applied

Scientific EffectPhotoconduction: Photoconductivity

Data Source

PatentUS10468450B2Apparatus for radiation detection in a radiography imaging system

Publication Date: 2019.11.05 DOSE SMART IMAGING

AI summary

This disclosure is directed at a photoconductive element for a digital X-ray imaging system which consists of a detector element comprising at least one semiconducting layer for absorbing photons, a first electrode coupled to a surface of said semiconducting layer, a second electrode coupled to a surface of said semiconducting layer, wherein said first electrode and said second electrode are separated horizontally, and at least one of said electrodes is electrically isolated from said semiconducting layer by an insulating layer; a readout circuit element coupled to said detector element; and a dielectric layer between said detector element and said readout circuit element.