CdZnTe Detector Polarization Management via Parameter Optimization

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Solution Overview

Problem

CdZnTe detectors face challenges in handling high count rates due to space charge buildup, leading to polarization and count paralysis, which limits their application in high-flux imaging applications like medical Computed Tomography.

Innovation Solution

A CdZnTe photon counting detector design that selects optimal material properties and design parameters, including hole mobility, de-trapping time, bias voltage, temperature, and thickness, to maximize sustainable photon flux while avoiding polarization, using the equation Φγ*=ɛczt⁢ɛ0⁢V2qL⁢E_γ⁢λ2⁡[β-Lλ⁢exp⁡(-Lλ)]-1⁢μh⁢τhτh+τD, to ensure efficient charge dissipation and prevent polarization.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If high photon flux is applied to CdZnTe detector, then imaging speed and productivity are improved, but space charge buildup causes polarization and count paralysis

Engineering Contradiction:

Improvephoton flux handling capabilityVSAvoiddetector stability

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies parameter changes by optimizing the hole mobility-lifetime product (μhτh) and de-trapping time (τD) through material composition control (Cd1-xZnxTe where 0≤x<0.2) and operating condition adjustment (bias voltage V, temperature T). These parameter modifications enable the detector to sustain higher photon flux rates while preventing space charge polarization, directly resolving the contradiction between productivity and reliability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements dynamics by making the detector operating characteristics adjustable through bias voltage and temperature control. The de-trapping time τD is made temperature-dependent (τD ∼ exp(EA/kT)), allowing dynamic adaptation to different flux conditions. This enables the detector to maintain reliable operation across varying productivity requirements.

Inventive Principle:

Principle #15Dynamics

2Quantity of substance

If detector thickness L is increased, then photon absorption capability is improved, but charge dissipation rate decreases leading to higher polarization

Engineering Contradiction:

Improvephoton absorption capabilityVSAvoidcharge throughput rate

Core Design Contradiction:

Quantity of substanceVSProductivity

Solution Approach 1:

The patent resolves this contradiction through parameter changes by optimizing the relationship between thickness L and the hole mobility-lifetime product μhτh. The design equation Φγ*=ɛcztɛ0V2qLE_γλ2[β-Lλ]−1/μhτhτh+τD shows that for a given flux capability, thicker detectors can be compensated by adjusting μhτh and other parameters. This allows optimization of absorption capability while maintaining charge dissipation rate.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If bias voltage V is increased, then charge dissipation rate is improved, but energy consumption increases

Engineering Contradiction:

Improvecharge dissipation rateVSAvoidbias voltage energy consumption

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent applies parameter changes by optimizing the bias voltage V in relation to other detector parameters (thickness L, hole mobility-lifetime product μhτh, de-trapping time τD). The design equation shows that V can be adjusted to achieve required charge dissipation rates while minimizing energy consumption, resolving the contradiction between productivity and energy usage.

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 design enables CdZnTe detectors to handle photon fluxes exceeding 20 million counts/s/mm2 without polarization, significantly enhancing their performance in high-flux imaging applications by effectively managing charge transport and electric fields.

Implementation Method 1

charge generated by photon flux, e.g., x-ray radiation, in the CdZnTe crystal structure

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

charge generated by photon flux, e.g., x-ray radiation, in the CdZnTe crystal structure thereof is dissipated at a sufficiently high rate, through both drift and recombination

Methodology Applied

Scientific EffectDrift: Electrophoresis

Implementation Method 3

charge generated by photon flux, e.g., x-ray radiation, in the CdZnTe crystal structure thereof is dissipated at a sufficiently high rate, through both drift and recombination

Methodology Applied

Scientific EffectRecombination:

Data Source

PatentUS7705319B2CdZnTe device using constrained design for high-flux x-ray spectroscopic imaging applications

Publication Date: 2010.04.27 EV PRODUCTS INC

AI summary

A CdZnTe photon counting detector includes a core material of Cd1-xZnxTe, where (0≦x<1), an anode terminal on one side of the core material and a cathode terminal on a side of the core material opposite the anode terminal. At least one of the following is selected in the design of the detector as a function of the maximum sustainable photon flux the core material is able to absorb in operation while avoiding polarization of the core material: electron lifetime-mobility product of the core material; de-trapping time of the core material; a value of a DC bias voltage applied between the anode and the cathode; a temperature of the core material in operation; a mean photon flux density to be absorbed by the core material in operation; and a thickness of the core material between the anode and the cathode.