Apr 4 2008
Sunovia Energy Technologies, Inc. is pleased to announce technology and manufacturing breakthroughs by EPIR Technologies, Inc. (EPIR). EPIR's research and development efforts have formed a cornerstone for products that enabled the U.S. military's night vision superiority. The breakthroughs address cost reductions that further enable infrared (IR) sensors for use in large commercial markets and provide a new paradigm for multi-junction solar cells. The new solar cell technology will have high efficiencies at lower costs by leveraging less expensive IR system materials and manufacturing processes that have been developed with more than $30 million dollars of investment over the past 25 years. Sunovia and EPIR believe that a very successful strategy is to leverage the ongoing commercialization and continued sale of advanced IR sensors while directly transferring these breakthrough IR technologies to the commercialization of next-generation solar cells. A portion of the core technologies behind EPIR's breakthroughs are disclosed in U.S. Patent No. 6,657,194, "Multispectral Monolithic Infrared Focal Plane Array Detectors".
Dr. T. S. Lee, who joined EPIR from the Microphysics Laboratory (MPL) at the University of Illinois at Chicago (UIC), was responsible for many of the technical breakthroughs needed for this work. Dr. Lee stated "We surmounted many technical hurdles such as the MBE growth of CdTe and HgCdTe layers on heterostructural silicon wafers containing readout integrated circuits to successfully mate II-VI semiconductor materials with Si for device fabrication for x-ray and infrared detection. I am very excited that this technology also has solar power applications, where it can play a major role in reducing the world's demands for fossil fuels."
"Owning the Night" has been a cornerstone of maintaining the U.S. Army's tactical superiority through advanced technology, plans and tactics. A key element in this equation is maintaining and expanding a clear technological edge in the area of IR imaging -- night vision. Improving sensitivity, decreasing noise, enhancing reliability, and lowering costs represent important success factors in this effort. Central to this work has been the very innovative and extensive research and development work of professor Siva Sivananthan and his teams at UIC, and at EPIR. The most significant advances over the last two and a half decades in the area of advanced materials for IR imaging have come out of the labs of UIC and EPIR.
In the area of night vision, enabling successful nighttime operations lies in the ability to widely disseminate cutting edge imaging technology to as many of the soldiers as possible involved in these nighttime operations. An impediment to accomplishing this goal has been the high cost of these IR imaging devices. The delicate nature and high cost of the MCT IR light detection material itself has been the prime culprit. This advance in depositing a very thin layer of ultra-sophisticated material directly on the read out circuitry represents the removal of a significant hurdle towards achieving substantially lower cost finished devices and systems.
Specifically, EPIR's achievement is a MCT IR focal plane array (FPA) grown directly on a thin cadmium telluride (CdTe) epilayer, which in turn was grown directly on a silicon (Si) read out integrated circuit (ROIC). Thus, the infrared focal plane array that generates the electrical signals to be converted into a digital picture was directly and monolithically connected to the ROIC that interprets those signals to create a picture, without a need for externally applied contacts and interconnects. This monolithic integration of an MCT FPA with its ROIC simultaneously realized a key differentiator within IR detector technology and formed a proof of concept for the fabrication of a novel high efficiency, two-junction and two-terminal solar cell.
This breakthrough resulted from many years of intensive work on the molecular beam epitaxial (MBE) growth of CdTe on Si and of MCT on CdTe, first at MPL and then by many of the same scientists and engineers at EPIR. One of the major challenges overcome was the cleaning of the Si ROICs without damaging the contacts or resorting to temperatures high enough to damage the ROICs. Another was the direct deposition of high quality single crystal CdTe directly on the Si ROICs with excellent current collection by the ROICs despite the small fractional area available for growth on ROICs. Yet others were the deposition of high quality single crystal MCT on the CdTe and the dopant activation and device processing to create an FPA, all at temperatures low enough not to harm the ROIC. Overcoming these challenges clearly demonstrated the ability to fabricate multijunction, two-terminal high- efficiency solar cells such as CdTe/Si cells or other more complex cells based on CdTe/Si and went far beyond that demonstration. This breakthrough and much other work by EPIR on IR FPAs has clearly demonstrated the ability to fabricate such solar cells with the necessary current matching and efficient current collection, without a buffer layer between the Si and the CdTe, with or without a thin zinc telluride tunneling barrier as needed for current matching.
Monolithic integration such as that achieved by EPIR obviates all of the deficiencies associated with the usual bump binding between the contact on each pixel of an FPA and the corresponding ROIC contact, eliminates complex and low-yield processes, eliminates thermal mismatches and thus allows much larger formats and greater resolution, creates compact systems with lower heat loads, and reduces costs by increasing yield. Non-monolithic FPAs, whether grown on Si or on cadmium zinc telluride (CZT) suffer from many deficiencies because of the necessary bump-bonding This bump-bonding requires extensive packaging, is susceptible to vibration failures and is plagued by parasitic capacitances and inductances that degrade the sensitivity and bandwidth of the FPAs.
The material grown and the monolithic devices fabricated were subjected to a number of tests and passed all of them. For example, the measured carrier recombination time, which is the primary measure of material quality and must be long enough to allow the currents generated by incident light to be efficiently collected, was excellent. Also the measured dynamic FPA impedance at the standard operating temperature of 80 K reached 10(6) Ohm-cm(2) at zero bias for growth on Si and 10(5) Ohm-cm(2) for growth on ROICs, again excellent values. Finally, the device operability was found to be excellent, although a small fraction of the pixels lost operability during device fabrication.
In addition to defense IR imaging applications and markets, much larger markets exist in providing a night vision / IR imaging capability in security, law enforcement, and spectroscopic imaging applications. Sunovia believes this significant cost saving advance will go far in enabling the widespread adoption of this technology into these new markets and applications.
Sunovia and EPIR have exclusively partnered to commercialize solar, IR and x-ray technologies for the renewable energy, night vision and medical and scientific markets. Sunovia is the exclusive marketer of all products, technologies and intellectual properties that are developed by EPIR, and currently owns a significant equity interest in EPIR. EPIR is the world leader in R&D on materials and devices for IR detection and imaging for night vision, missile tracking, exploration in space and other applications.
Sunovia announced today that Donna Webb has been appointed to the position of vice president of operations. The company mistakenly indicated that Mrs. Webb had been appointed to the position of chief operations officer in a press release dated March, 2008.