A germanium charge-coupled device (CCD) offers the advantages of a silicon CCD for X-ray detection – excellent uniformity, low read noise, high energy resolution, and noiseless on-chip charge summation – while covering an even broader spectral range. Notably, a germanium CCD offers the potential for broadband X-ray sensitivity with similar or even superior energy resolution than silicon, albeit requiring lower operating temperatures (≤ 150K) to achieve sufficiently low dark noise due to the lower band gap of this material. The recent demonstration of high-quality gate dielectrics on germanium with low surface-state density and low gate leakage is foundational for realization of high-quality imaging devices on this material. Building on this advancement, MIT Lincoln Laboratory has been developing germanium CCDs for several years, with design, fabrication, and characterization of kpixel-class front-illuminated devices discussed recently. In this article, we describe plans to scale these small arrays to megapixel-class imaging devices with performance suitable for scientific applications. Specifically, we discuss our efforts to increase charge-transfer efficiency, reduce dark current, improve fabrication yield, and fabricate backside-illuminated devices with excellent sensitivity.
Silicon charge-coupled devices (CCDs) are commonly utilized for scientific imaging in wavebands spanning the near infrared to soft X-ray. These devices offer numerous advantages including large format, excellent uniformity, low read noise, noiseless on-chip charge summation, and high energy resolution in the soft X-ray band. By building CCDs on bulk germanium, we can realize all of these advantages while covering an even broader spectral range, notably including the short-wave infrared (SWIR) and hard X-ray bands. Since germanium is available in wafer diameters up to 200 mm and can be processed in the same tools used to build silicon CCDs, large-format (>10 MPixel, >10 cm2 ) germanium imaging devices with narrow pixel pitch can be fabricated. Furthermore, devices fabricated on germanium have recently demonstrated the combination of low surface state density and high carrier lifetime required to achieve low dark current in a CCD. At MIT Lincoln Laboratory, we have been developing germanium imaging devices with the goal of fabricating large-format CCDs with SWIR or broadband X-ray sensitivity, and we recently realized our first front-illuminated CCDs built on bulk germanium. In this article, we describe design and fabrication of these arrays, analysis of read noise and dark current on these devices, and efforts to scale to larger device formats.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.