Symmetric cubic diodes give a directionally independent response

ProjectNew radiation detectors for quality control of radiation therapy

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New radiation detectors for quality control of radiation therapy

A novel X-ray detector diode, optimized for angular independent response, has been developed. The diode is designed as a silicon cube with p-n junctions on all six sides, which creates a device that is close to being symmetrical in 3D.

The application of the X-ray detectors is an instrument for verification and quality control of dose distribution in radiation therapy systems, manufactured by the company ScandiDos AB in Uppsala. In this instrument, discrete detector diodes are arranged in a 3D-matrix inside a body phantom. The conventional “pizza box” shaped detector chips used today have an undesired directional dependence in the response, and the objective of the project is to develop a novel X-ray detector diode with directionally independent response. The idea is that this result will be achieved by a symmetric cubic diode design.
The cube edge is 300-400 µm. The manufacturing process is based on micromachining, featuring deep reactive ion etching (DRIE) of silicon-on-insulator (SOI) substrates, doping of vertical walls from gas phase dopants and re-fill of etched trenches with polysilicon.