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Last, but not least, EEV (English Electric Valve). Obviously we have lots of contact with this UK company (part of the GEC group). They have a low profile in the US which is a pity. We have used five of their 05-xx series devices, of format. They work very well, except that they have not been available in a thinned form to date. A short performance summary of EEV (thick) CCDs:-
noise measured on the telescope, 50% (thick) peak Q.E., grade-1 cosmetics (no bad columns, small traps), excellent CTE at .
So far the largest device they have made is the CCD05-50, pixels. They are therefore confident about making a device as large as , with good yields.
EEV have worked already on thinning small, TV type sensors with some success and it was hoped that they could, on a reasonable time scale, provide us with the same sort of performance from larger format, smaller pixel devices. Recently (early 1993) EEV have considerably advanced their thinning techniques (under a contract from the European Space Agency) to provide detectors for the MERIS (Medium Imaging Earth Resources Satellite) programme; this work has made them feel confident in offering a large-area thinned device commercially.
EEV have offered to make some , thinned chips- with some guarantees of performance; payment would not be made if they fail. The chip design would be very similar to previous devices and would permit multi-edge butting. Our first requirement is for about four single (spectroscopic) chips, of this sort of size. If these devices work well we would then expect to get some buttable versions for imaging soon afterwards.
We have been testing samples of recent EEV thin devices- a (MERIS) thinned CCD. We had hoped that this would prove that they really have solved the thinning problem on a large-area device. Their initial confidence was not however, borne out by tests here at the RGO. Our cryogenic tests showed considerable non-uniformity and poor UV response which they attributed to over-etching (especially in the centre). Their tests of the MERIS chips, made at room temperature, had not detected this problem. They believe that by more rigorous control of the etching depth, they ought to achieve better results- and attain the crucial high spectral response over the whole area. We are currently waiting for further sample chips to test.