Germanium Wafers: August 2018

Aug 16, 2018

A germanium hybrid pixel detector with 55μm pixel size and 65,000 channels

Hybrid pixel semiconductor detectors provide high performance through a combination of direct detection, a relatively small pixel size, fast readout and sophisticated signal processing circuitry in each pixel. For X-ray detection above 20 keV, high-Z sensor layers rather than silicon are needed to achieve high quantum efficiency, but many high-Z materials such as GaAs and CdTe often suffer from poor material properties or nonuniformities. Germanium is available in large wafers of extremely high quality, making it an appealing option for high-performance hybrid pixel X-ray detectors, but suitable technologies for finely pixelating and bump-bonding germanium have not previously been available.

A finely-pixelated germanium photodiode sensor with a 256 by 256 array of 55μm pixels has been produced. The sensor has an n-on-p structure, with 700μm thickness. Using a low-temperature indium bump process, this sensor has been bonded to the Medipix3RX photoncounting readout chip. Tests with the LAMBDA readout system have shown that the detector works successfully, with a high bond yield and higher image uniformity than comparable high-Z systems. During cooling, the system is functional around -80°C (with warmer temperatures resulting in excessive leakage current), with -100°C sufficient for good performance.

Source:IOPscience

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Aug 3, 2018

Electron beam generated phase zone plates with 30 nm zonewidth for high resolution X-ray microscopy

The authors report the manufacture of germanium phase zone plates as objective lenses for high resolution X-ray imaging at 2.4 nm wavelength. The phase shifting properties of the germanium can be used to enhance the diffraction efficiency of a zone plate. Zone plate patterns with structure widths down to 30 nm are generated by low distortion electron beam lithography. The structures are transferred into a 280 nm thick layer of germanium by reactive ion etching (RIE) using a highly selective trilevel mask. 100 nm thick boron doped silicon windows made from single crystal wafers serve as high transmission support membranes. Measurements at the BESSY storage ring proved diffraction efficiencies up to 6.2%. X-ray imaging of a test object showed clearly resolved 30 nm features.