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A pixel readout chip for X-ray imaging has been developed and tested. It will he used in a hybrid pixel detector, where it is flip-chip bonded to a sensor. The sensor material can be silicon or a compound semiconductor, such as CdZnTe. A novel feature of the chip is the implementation of two counters inside each pixel cell. The chip consists of 992 pixels arranged in 31 columns and 32 rows. Each pixel size is 270 micrometer square and it consists of a preamplifier, shaper, discriminator and two counters. The circuit design with two integrated counters in each pixel cell makes it possible to acquire two images very close in time with practically no dead time in between. An externally adjustable threshold permits the discrimination of a portion of the X-ray spectrum. The detector is primarily aimed for dynamic medical X-ray imaging up to 100 frames per second. A characterization of the performance of the chip is presented and discussed.

A semiconductor hybrid pixel detector for dynamic X-ray imaging is being developed. The detector consists of a 500 /spl mu/m thick silicon sensor and a pixel readout chip. The two parts are interconnected by means of anisotropic conductive film. The basic building block of the detector is approximately one square centimeter large and consists of 992 pixel cells arranged in 31 columns and 32 rows. Each pixel has an area of 270 micrometer square and the readout chip contains amplifier, discriminator and two 12 bit counters. An externally adjustable threshold level can be changed within one microsecond from one image to another in order to select different parts of the X-ray spectrum. The chip can be tuned to assign different weighting functions to photons with energies exceeding the threshold. It is possible to either operate the detector as a photon counter or as an energy integrator.

Silicon strip detectors with double-sided readout have been designed and processed on 100-mm silicon wafers. Detectors with integrated coupling capacitors and polysilicon bias resistors were tested by static electrical measurements. A detector with VLSI readout electronics was measured in a test beam. Test beam measurements show signal over noise ratios of 39 on the detector p-side and 26 on the n-side. >

A fast high-resolution hybrid silicon pixel detector is being designed at Uppsala University as a part of on digital X-ray imaging (DIXI) project. The pixel size is 250/spl times/250 /spl mu/m/sup 2/ and the first design aims at an overall area of 128/spl times/128 mm/sup 2/ with a total of 262k pixels. The readout electronics will be connected to the sensor array via bump bonding. Each pixel contains implemented logic for preprocessing and registration. A prototype 0.5 mm thick Si sensor with 16/spl times/8 pixels is processed, a 1 mm version has been ordered, and a readout chip with 8/spl times/8 pixels is in production.