New biaxial flexure test device for ultra-thin germanium

Germanium is a semiconductor now widely used in gamma and X-ray detectors and high-performance space-based solar cell arrays and is also being developed for land-based solar cell applications. Growth and processing of germanium and other semiconductor crystals, without the generation of defects, is a critical issue in electronic materials processing and device manufacturing. In order to reduce the high costs, the germanium single crystal wafers are generally cut ultrathin. This creates a relatively large width-to-thickness ratio making the wafers very susceptible to mechanical stresses during processing. Therefore, knowing the stress criteria for fracture during handling is vital in order to prevent any micro-cracks or total wafer failure. A new biaxial flexure testing device was designed and fabricated for full wafer testing of thin germanium wafers. The new device allows for a controlled and uniform application of very small loads, and continuous measurement of the deflection. The test setup is simple, inexpensive, easy to setup and use, and can be easily modified for a wide range of specimen types and sizes depending on the particular use. Thin germanium wafers of varying thicknesses and surface conditions were examined using this device. Three-point bend tests were also carried out and both these types of tests were then compared.