Large Periphery Aluminum Indium Gallium Nitride Metal Oxide Semiconductor Heterostructure Field Effect Transistor Device for High Power X-Band Microwave Amplifiers
 Summary:
Sensor Electronic Technology, Inc. (SET; Columbia, SC), is developing and commercializing advanced electronic devices called metal oxide semiconductor heterostructure field effect transistors (MOSHFETs) based on wide bandgap materials developed over the past several years through MDA's advanced technology and SBIR programs. SET is a spin out company from Rensselaer Polytechnic Institute, which held a subcontract from an MDA-funded effort at the University of South Carolina. SET’s device and materials research work has many applications in the defense and commercial sector. For MDA, the aluminum indium gallium nitride (AlInGaN) devices can be used to improve radar systems. On the commercial side, the technology has many applications spanning from commercial lighting to wireless communications. The company opened production facilities and is ramping capability to produce 2,000 2-inch wafers by the end of 2003.
Technology Description:
Over the past decade, industry and the U.S. Government have invested hundreds of millions of dollars in wide bandgap semiconductors. We know these materials have strong potential for defense and commercial use—but what are they really? The answer remains at the atomic level. A range of energies called the forbidden band separates the valence band and the conduction band of a solid-state material. The valence and conduction bands can hold electrons; however, no electrons may reside in the forbidden band. The wider the forbidden band, the more energy is required to excite an electron from the valence band into the conduction band. If a material has no forbidden band, it behaves as metal. If it has a very wide band, it is a good insulator. Semiconductors lie somewhere in the middle. When we speak of wide bandgap materials, we are referring to aluminum nitride, gallium nitride, silicon carbide, diamond, and other compound semiconductors that have a relatively wide forbidden band compared to silicon and gallium arsenide. This property allows the devices in which they are used to handle much higher power and voltage than silicon, and withstand and operate at much higher temperatures. Such materials also exhibit unique optoelectronic capabilities that allow them to emit blue and ultraviolet (UV) light.
Several companies and research institutes have worked in the area of wide bandgap semiconductors since the mid-1980s (depending on where and when one starts counting), especially in the area of silicon carbide and more recently, gallium nitride. Sensor Electronic Technology, Inc. (SET; Columbia, SC) is focusing on the wide bandgap materials, aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN) and their alloys, such as ternary aluminum gallium nitride (AlGaN) and indium gallium nitride (InGaN), and quaternary aluminum indium gallium nitride (AlInGaN). The company has developed proprietary material growth reactors, which combine the advantages of conventional metalorganic chemical vapor deposition (MOCVD) with novel growth process called pulsed atomic layer epitaxy (PALE). Using a patent-pending technology, the company is producing AlInGaN material wafers for manufacturing of devices called metal oxide semiconducting heterostructure field effect transistors or MOSHFETs.
The devices address many of the problems that researchers working in wide bandgap semiconductors are grappling with today. At present, nearly all the development work has focused on conventional AlGaN/GaN high electron mobility transistor (HEMT) devices on sapphire and insulating silicon carbide substrates. But several key problems impede commercial development of these devices, such as gate leakage and current collapse, which reduce power output at microwave frequencies.
By using PALE to deposit AlInGaN, the researchers can pulse the material into the system and deposit layer by layer at reduced temperatures, thus forming a high-quality heterointerface between the various layers of the device. Owing to the proprietary process for deposition of high-quality silicon dioxide layers on AlInGaN, gate leakage is reduced by four to six orders of magnitude, saturation current goes up, and DC and RF characteristics stay the same as, or are even better than, those for conventional HEMTs. SET was awarded two more MDA SBIR Phase I contracts to develop a double heterostructure field-effect transistors (DHFETs) on SiC and bulk AlN substrates to address current collapse. By combining the two technologies, the company will be able to make devices that address gate leakage and current collapse. Initial testing in March 2002 provided very promising results.
Another aspect of the work revolves around strain engineering. Covalent bonding between elements of different particle sizes causes strain in the material system that can lead to inefficiencies or failures in the finished device. By engineering the bonding configuration so that it “balances out,” the researchers are able to reduce the strain in the devices thus improving their performance characteristics and reliability.
MDA Origins:
This work, if successfully and fully developed, could significantly improve radar systems, serving as a better alternative to cathode ray tubes and gallium arsenide devices. Devices made from AlInGaN theoretically will last significantly longer than cathode ray tubes while also being much smaller and requiring less cooling power. In addition, they will provide higher power capabilities than their gallium arsenide counterparts.
MDA originally funded research on PALE and strain engineering at the University of South Carolina through Dr. Asif Khan. Some of this work was subcontracted to Rensselaer Polytechnic Institute (RPI) through Dr. Michael Shur and Dr. Remis Gaska, and significant collaboration took place between the two Universities.
Dr. Remis Gaska and Dr. Michael Shur assisted in spinning out the small business, which then received MDA SBIR Phase I and II contracts to perform the MOSHFET work, as well as a Phase I contract to develop a double heterostructure field-effect transistor to address current collapse. Five more Phase I contracts related to this effort have been awarded by the MDA SBIR program in January-February of 2003.
Spinoff Applications:
Aside from increasing power levels and reducing the size of MDA's radar systems, SET’s AlInGaN materials can serve as an improvement for a host of commercial applications such as wireless communications, serving to transfer more information at higher efficiencies than gallium arsenide microelectronics at satellite or ground base stations.
AlInGaN optoelectronic devices can also be used for air and water purification, bio-agent detection and in medical applications. For example, the technology can be used for phosphorescent imaging, photodynamic therapy, or in the treatment of Seasonal Affected Disorder (SAD).
In addition, AlInGaN materials can be used in diode arrays as solid-state sources for general lighting of residences, offices, retail operations, and industrial facilities, offering a much longer lasting and energy efficient source for illumination. This important enabler could revolutionize the entire lighting industry by replacing existing incandescent and fluorescent lighting with a brighter, smarter (because it is digital) and far more energy efficient alternative. One study suggested that white LEDs, if fully implemented, would save up to $115 billion per year in electricity by year 2015, thus reducing air pollution and other waste generated by power plants. While this industry is in its infancy, the first demonstrations of LED-based technology have recently occurred, first at an Austrian company, Barenbach Lighting Laboratory in 2000 and in a LED-based household lighting project implemented in 2001 in remote communities of Nepal (142 households and two schools). Interestingly, the lamps successfully superseded the kerosene wick lamps and burning sap-filled pine sticks used by the communities due to their low electricity consumption. However, a breakthrough of LED-based technology in general lighting is expected to occur when the luminous efficiency of solid-state sources approach 200 lumens per Watt, but could occur at lower efficiencies if environmental or energy-saving issues become more pressing.
Commercialization:
Originally located in Latham, NY, SET spun out from MDA University projects at Rensselaer Polytechnic Institute and University of South Carolina. In August 2002 SET has moved its headquarters to Columbia, SC, to be closer to its university collaborator, Dr. Asif Khan, at the University of South Carolina. The company currently has 14-employees, with 11 located at the South Carolina site.
SET is pursuing three key commercial areas: (1) RF electronics for radar and wireless communications, such as ultra-high power base stations and satellite communications; (2) ultraviolet light emitters for bio-agent detection, biomedicine, and water/air purification systems; and (3) solid-state lighting. The company’s goal is to become a major supplier of materials and devices for emerging high-power RF electronic, visible ultraviolet optoelectronic, and solid-state lighting markets.
DoD and commercial entities are evaluating transistor wafers that SET shipped this year, produced at its South Carolina facility. The company expects to have the capability to produce 2,000 2-inch wafers by the end of 2003. At this rate, market demand will still greatly exceed production capability.
Recent Phase I contracts (May FY’02 solicitation) have resulted in collaborations with major players in the advanced materials area. II-VI, Inc. has collaborated on two Phase Is, where the company will provide SET with silicon carbide substrates for use with SET’s AlInGaN devices. In addition, SET is collaborating with EMCORE, which is providing new instruments for precisely measuring film thickness and temperature during the growth. SET will use this instrumentation in the production of their AlInGaN wafers.
Company Profile:
SET was established in 1999 by Drs. Remis Gaska and Michael Shur to transfer and commercialize the technology funded at RPI and the University of South Carolina. The 14-employee business based in Columbia, SC, also has an office in Latham, NY. SET maintains collaboration with the University of South Carolina (Dr. A. Khan). In addition, the company is a part of DARPA’s wide band gap semiconductor program, has two 3-year contracts with the U.S. Army (non-SBIR), as well as a Phase II contract from ONR and a Phase I contract from DARPA. The company has also worked with another MDA SBIR-funded company, Crystal IS (Latham, NY), which supplied SET with unique bulk AlN substrates.
Contact Information:
Dr. Remis Gaska
Sensor Electronic Technology, Inc.
1195 Atlas Road
Columbia, SC 29209
Tel:(803) 647-9757
Fax:(803) 647-9770
email: gaska@s-et.com
web: www.s-et.com
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