Warfighters are increasingly exploiting electronic systems to achieve force multiplication. The performance and price of components in these systems depend directly on the reproducibility, quality, and cost of electronic materials synthesis and processing. Electronic materials science also is the enabling technology for electronic and EO devices, whose payoffs include higher maintainability, lighter weight, smaller volume per function, higher data rate processing, and higher frequency/bandwidth operation—characteristics essential for establishing military dominance in areas such as avionics, radar, C4I, guidance, target identification, surveillance, and navigation. For example, development of III-V semiconductor substrate and films/nanostructures will make more compact radars and higher frequency and data rate communication systems possible in the mid term (3-5 years). In the mid and long terms, materials for IRFPAs will make possible modules capable of broader band detection, multiple color response, and room temperature operation; wide-bandgap semiconductors will make electronics available that operates at 300-500°C (e.g., near engine components), as well as compact ultraviolet laser systems for full-color display applications and high-density optical data storage. Because electronic materials technologies are inherently dual use, DoD programs will benefit civilian electrotechnology, whose enhanced capabilities will benefit military technologies in time.
3.9.2.1 Goals and Timeframes. The electronic materials subarea develops materials, fabrication processes, and device structures that are not supported commercially; are necessary for developing RF, microelectronics, and EO devices and components; and combine affordability with high performance for use in DoD systems. Major goals are listed in Table VII-10.
| Fiscal Year | Goal |
|---|---|
| FY98 | Demonstrate 3-inch diameter substrate wafers of 4H and 6H SiC with uniform doping and defect density < 103/cm2 across the entire wafer; high-resistivity SiC substrates. Develop controlled p-doping of GaN epitaxial films. Develop reproducible epitaxial growth of doped and semi-insulating, low-defect density (<105/cm2) GaN. Demonstrate reliable shallow p-type doping technology for epitaxial growth of GaN. |
| FY99 | Develop a commercially viable SiC epitaxy process that yields materials properties (defect density, control of dopants) that exceed substrate quality. Develop a means to synthesize GaN substrates of 1 inch or greater diameter. Develop effective doping of high aluminum alloy ratio AlGaN material. |
| FY01 | Demonstrate substrates for high-quality films of Group III nitride (III-N) and II-VI semiconductors. |
3.9.2.2 Major Technical Challenges. Most electronic materials efforts are linked by the need to reduce the concentration of deleterious defects; to control material composition (including intentional, judicious introduction of impurities), structure, and morphology in order to tailor properties; and to develop fabrication and characterization methods that result in high-quality materials at affordable prices. Additional challenges depend on specific materials and the maturity of the technology. The near-term challenge for high-temperature semiconductors and HTS materials, both of which are at early stages of development, is to produce material having properties suitable for demonstration devices and small-scale components. Substrates that match the lattice constants and thermal expansion coefficients of III-N films are especially needed. For the more nearly mature GaAs- and InP-based materials, challenges include fabrication of larger diameter substrates having lower defect densities, higher uniformity, and lower cost; further control and exploitation of the relationships among growth environments and resulting properties—particularly controlling heterostructure interfaces such as InGaAs/InP; and minimizing the strain induced by lattice mismatches between constituents of the heterojunctions. Key technical challenges for IR detector materials are the achievement of greater uniformity, more precise process control, and, for heterostructure detectors, control of interfaces and strain.
3.9.2.3 Related Federal and Private Sector Efforts. AT&T, Hewlett-Packard, Texas Instruments, Raytheon, Lincoln Labs, Hughes, and several universities have important III-V epitaxy programs. NIST works with AF-RL/ERX and AF-WL/ELD to characterize wafers manufactured by contractors in the Title III GaAs substrate program. M/A-COM, Litton Airtron, and AXT market GaAs substrates; Crystacomm and AXT produce InP substrates. (No company, however, conducts significant internally funded R&D.) Hewlett-Packard, APA Optics, ATMI, and some universities conduct important III-N work. Cree, Westinghouse, and North Carolina State University fabricate SiC. NASA, NIST, LANL, Sandia, ANL, Lincoln Labs, AT&T, IBM, Westinghouse, Conductus, Superconductor Technologies, Dupont, and several universities have important HTS programs.
The electronic materials subarea is directed toward the development of new materials and the improvement of existing materials intended for device applications. Device/component performance and reduced cost are the benchmarks of success. This subarea encompasses substrate development, epitaxial growth, dopant incorporation and control, control of interface abruptness and quality, bandgap engineering, and development of materials/device interfaces and structures. Materials development supports device development thrusts by providing quick turnaround of materials growth and characterization, the ability to tailor growth and processing techniques to optimize parameters, and development of processing materials and techniques. Classes of interest include semiconductor, superconductor, ferro/ferrimagnetic, ferroelectric, and nonlinear optical (NLO) materials.
3.9.3.1 Technology Demonstrations. The electronic materials subarea is primarily an enabling technology. Upon optimization of materials and processes, the growth or processing technology is transitioned to device development projects and to industry for scale-up or commercialization. Thus, electronic materials technologies are "demonstrated" by successful transitions into the device/component community.
3.9.3.2 Technology Development. By targeting high-leverage technologies, notably materials technologies that have diverse electronic and electro-optic applications, this subarea anticipates the needs of the DoD electron device and component communities. Key areas of investment are summarized below.
Wide-Bandgap Electronic Materials Technology (DTO SE.39.01). The focus is on growth of large-area SiC substrates for high-power RF and high-temperature electronics; on use of (Al,Ga,In)N materials for these electronic applications; on producing and detecting green, blue, and ultraviolet light; and on creating field-emitting arrays. The III-N efforts include growth of lattice and thermally matched substrates (e.g., ZnO and Li aluminate, as well as high-risk, high-payoff efforts to grow GaN as a substrate) and also of films and heterostructures by OMCVD and MBE techniques. This DTO directly supports Joint Theater Missile Defense DTO D.04, Advanced X-Band Radar Demonstration.
Intermediate bandgap III-V semiconductors efforts include development of advanced InP substrates; III-V films, heterostructures, and nanostructures grown on GaAs and InP substrates by OMCVD and MBE; and SiGe heterostructures for RF HBTs. GaAs-based materials development is being pursued because GaAs still dominates microwave electronics and because certain GaAs-based ternary alloys have been identified as candidates for high-speed applications. InP-based materials (plus antimonides) are being developed for very high frequency/high data rate applications (300-GHz transistors are possible) and for possible displacement of GaAs in high-power and low-noise microwave applications. InP-based materials are, moreover, the mainstay of optoelectronics for telecommunications. Thus, they are being developed for optically implemented control functions (e.g., of radar antenna remoting and true time delay control of phased array antennas), as well as for communications applications and OEICs.
IR detector materials are being developed for applications that include IRFPAs for surveillance and night/all-weather operations. Films and structures based on InAs/GaSb super-lattices (capable of detecting wavelengths >12 µm) and SiGe (for Schottky barrier devices) are being developed in pursuit of these goals. Work in the high-temperature superconductivity area emphasizes development of YBa2Cu3O7 films and structures whose near-zero electrical resistance can be exploited to create extraordinarily narrowband filters and compact high-frequency, high-bandwidth antennas. Also under development are materials for mid-IR optical amplifiers and oscillators (e.g., for frequency-agile lasers), optical computing/storage, target identification, free-space optical interconnects, and optical data storage.
Patterning efforts include lithographic resists by self-assembled monolayers for creating device features <0.25 µm and proximal probe methods for nanoscale device patterning. Processing and equipment efforts, synergistically linked to semiconductor film/nanostructure deposition work described above, emphasize development and technology transfer of promising process technologies. Examples include the Desorption Mass Spectrometry feedback and the Linear Motion Oven for improving molecular beam epitaxy (MBE) yield; use of Sb surfactant, In pre-deposition, and flashoff in GaAs/InGaAs MBE growth; development and applications of a conical sputter source; and development and characterization of an OMCVD close-spaced reactor.
3.9.3.3 Basic Research: Basic research opens up fruitful new areas of exploratory development. Consistent with electronic materials' character as an enabling technology, many 6.2 efforts are strongly coupled to basic research tasks. Basic research is employed to create the knowledge base undergirding the exploratory development efforts; exploratory development efforts help direct basic research along high-impact paths, and may also generate specific technologies that enhance research work. Specific basic research material efforts that will enable key technology development are atomic control of structures, investigation of new concepts for growth and patterning of nanoscale device structures, and materials tailored for multiple spectrum sensors. Continued investigation of fundamental properties of wide-bandgap materials feeds directly into materials and device technology.
