In this Phase I proposal we will develop a cost-effective large-area high-sensitivity x-ray panel detector for digital mammography. This direct-conversion x-ray detector will dramatically improve the capability for cost- effective high-performance mammography. By growing polycrystalline CZT (cadmium zinc telluride) films directly onto custom CMOS readouts, we will create large area panels with high resolution and high sensitivity. These panels will provide cost-effective, high-performance detectors for many other x-ray imaging applications including general radiography, fluoroscopy, and x-ray CT. We will leverage our existing expertise in polycrystalline film growth, solid-state x-ray detector physics, and x-ray readout ASIC design to produce CZT (cadmium zinc telluride) films grown directly onto customized CMOS readouts. Recently, academic research groups in Korea and Japan have investigated the potential for polycrystalline CZT films grown directly onto readouts to create x-ray imaging panel detectors. These studies have shown that relatively low substrate temperatures can be maintained during the film growth, enabling direct growth onto readouts such as thin-film transistor arrays and CMOS devices. The films produced have shown good x-ray detection properties. We propose to extend this work in the U.S., using our own experience in mercuric iodide polycrystalline film growth for x-ray imaging detectors and our experience in designing and producing CMOS-based readouts compatible with direct growth of mercuric iodide films. In this Phase I we will develop the film growth apparatus and processes necessary for successful polycrystalline CZT film growth on ITO-coated glass slides and we will measure the x-ray detection performance. This will substantially reduce the risk for Phase II. In previous work, we have designed, fabricated, and coated large area (10 cm x 10 cm) imaging charge-integrating CMOS readout chips which are chemically compatible with mercuric iodide. In this work, we will adapt them for compatibility with the CZT film growth process. The readouts have 30 5m pixel grids, enabling high-resolution imaging, and 8 parallel outputs which produce an 8 frames per second readout speed for the 10 Mpixel device. In Phase II, the CZT-coated CMOS readouts will be tested for x-ray imaging characteristics. Most digital mammography systems have spatial resolutions limited by their use of indirect detectors - scintillators coupled to photodiode arrays. A few recent systems are based on amorphous selenium, a direct detector. However, even these systems are limited to pixel sizes of about 70-100 5m. The CMOS readouts which will be coated in Phase II incorporate 30 5m pixel grids, giving mammography and other x-ray imaging modalities access to higher spatial resolutions. The devices will also be cost-effective due to the approach of growing CZT films directly onto readout arrays. We will widely market the device as an OEM component to mammography system manufacturers.
We will grow a high-sensitivity detector material, cadmium zinc telluride (CZT), directly onto CMOS technology megapixel readouts. This will achieve significant breakthroughs in x-ray imaging panel detector price and performance. Mammography will benefit due to the improved spatial resolution and reduced cost from this unique combination of detector material and readout.
