Sensors and Electron Devices Directorate
The Panel on Sensors and Electronic Devices is charged to review the research activity of the Sensors and Electron Devices Directorate (SEDD). The panel met at the Army Research Laboratory (ARL) facility in Adelphi, Maryland, on July 13-16, 2009, and June 2-4, 2010. During those two meetings, the panel reviewed research portfolios in all four SEDD divisions: Electro-Optics and Photonics, Energy and Power Generation, Radio Frequency and Electronics, and Signal and Image Processing.
The review focused on both internal research projects and collaborative activities. SEDD is currently participating in Collaborative Technology Alliances (CTAs) in Robotics, Network Sciences, Cognition and Neuroergonomics, and Micro-Autonomous Systems and Technology (MAST). It also has several research centers and institutes focused on flexible displays, fuel processing, biotechnology, nanoscience, and microelectronics manufacturing. SEDD also participates in the International Technology Alliance (ITA) program.
CHANGES SINCE THE PREVIOUS REVIEW
Although the number of scientists and engineers at ARL has changed little since the previous review by the Army Research Laboratory Technical Assessment Board (ARLTAB), the fraction of technical staff that have earned doctorate degrees is trending up and is now approaching 50 percent. ARL management has adopted a well-conceived planning process that links institutional goals to strategic hiring goals. Within SEDD, strategic competencies among the staff are linked to addressing current and anticipated Army needs. The excitement and energy of the scientific staff are impressive. The directorate has clearly improved its ability to attract top-notch early-career scientists. Particularly notable are the doubling of
the number of postdoctoral fellows, from 12 to 24 since the previous review, and the staff turnover rate of around 10 percent per year.
There has been a similar improvement in the output of technical publications and patent disclosures. The average number of refereed technical publications in the 2 years since ARLTAB’s previous report1 has increased more than 29 percent. After a small drop in FY 2009, the number of new patent applications increased by 30 percent in FY 2010. In addition to publications, SEDD staff members have won a significant number of research and service awards both within the governmental service community and outside the laboratory.
Given that sensors and electronic device technology are constantly evolving, one of the expectations of SEDD is that it continuously update its research portfolio to keep pace with these changes. SEDD has addressed this expectation in the current, 2009-2010 reporting period by increasing its in-house research efforts in several areas, such as wide bandgap materials, image processing, flexible displays, and battery chemistries, while moving on from unattended ground sensors and sensor integration and transitioning silicon carbide (SiC) device research from in-house to external projects. More significant is that these changes are guided by a clearly stated long-term vision for each of the major SEDD mission areas. For example, the extreme energy and power vision describes an objective of providing the individual soldier with access to two to three augmented energy sources on the mesoscale and microscale. The heterogeneous electronics vision foresees intelligent systems built from multiple technologies integrated into clothing, vehicle surfaces, and other structures in the warfighter’s environment.
As research evolves, so must the facilities and equipment used to conduct that research. In the current reporting period, SEDD has invested $12.5 million in new equipment and laboratories. Most of these funds were spent on new and upgraded instrumentation, and investments were spread among all SEDD divisions.
Among the “crown jewels” of SEDD facilities are its extensive semiconductor fabrication lines. This facility has developed into an extraordinary research support tool capable of producing a diverse set of advanced semiconductor devices, all of which are critical to the ARL SEDD mission. However, the facility is in need of a major review even though it has been continuously upgraded since 2002. Much of the processing and support equipment is nearing the end of its useful life span. The maintenance status and the impact of the introduction of new process procedures need to be reviewed, and the SEDD management needs an independent, objective look at all of these issues and must be prepared to make significant investment in the near future to keep this capability at the cutting edge.
ACCOMPLISHMENTS AND ADVANCEMENTS
Energy and Power Generation Division
There has been a significant and encouraging change in vision in the Energy and Power Generation Division during this reporting period, reflecting the evolution of the energy and power field in general. There has also been a good deal of progress in addressing several challenging problems in the field. The division is organized into three branches: Electro Chemistry, Power Components, and Power Conditioning. Following are highlights of current research efforts in the branches.
The effort in reforming Jet Propellant 8 fuel (JP-8) to power (hydrogen or solid oxide) fuel cells is expected to net a total fuel-to-electrical efficiency of approximately 30 percent (about twice that of
conventional power generators). SEDD has taken an interesting approach to this problem based on a two-stage cleanup of fuel (removal of sulfur) and onboard reforming.
Battery research continues to be a strong area, and as a result the weight and effectiveness of the soldier’s battery load continues to improve. SEDD is pursuing several investigations, ranging from lithium-polycarbon fluoride-oxygen (Li/CFx-O2) hybrid batteries, a promising commercially available chemistry, to lithium air batteries, an exceptionally difficult set of challenges. Even the scaling of existing technologies into the soldier power domain has proven to be a big challenge. SEDD has had significant success during the past 2 years in addressing many of these challenges in soldier power.
In the area of SiC switching devices, SEDD has made and likely will continue to make important contributions to high-temperature power electronic systems at every level of technology, including capacitors, inductors, thermal management technology, circuit devices, and materials. Over the years SEDD has played a key role in the development of high-power/high-temperature electronics. The program is a good example of properly placed resources and persistence leading toward success.
The air core inductors project has achieved impressive performance, with inductance values and Q values that are quite high for the technology. The next step is to integrate this technology into a micro power converter. To that end, an approach based on nanodeposition by capillary action for on-chip inductors and capacitors has been proposed. In early stages, this technique has a potential payoff that is not limited to building energy storage components.
Radio Frequency and Electronics Division
The Radio Frequency and Electronics Division is focused on the development of next-generation electronic devices and sensors for Army systems operating in complex environments. Research in this division is organized into four branches: Micro- and Nano-Electronics Materials and Devices, Electronics Technology, Antennas and RF Technology Integration, and RF Signal Processing and Modeling.
The Micro-Autonomous Systems and Technology CTA is the centerpiece of the microrobotics research efforts in this division. The work is extremely impressive and demonstrates multiple capabilities to develop and/or integrate the very innovative advanced technologies required. Highlights of this system are these: (1) integration of the 250 GHz miniature 400 m range radar (developed by the University of Michigan), (2) the thin-film piezoMEMS (microelectromechanical system) bio-inspired wing, (3) the high-performance air-core MEMS inductors and transformers, (4) a novel nanoparticle delivery method for capacitor fabrication, and (5) nano-Rectanna for efficient energy harvesting. The MAST program is an excellent example of the role that SEDD should play in developing Army-centric technologies. It also highlights the fact that the nature of power and weight requirements is a moving target and requires constant collaboration.
Some of the most innovative research in SEDD is the piezoMEMS actuators for the microrobotics effort. It has certainly advanced the state of microstructures. Two important features were incorporated here: first, the use of the piezoMEMS processing capability to create the low-power micromotion; second, the construction of a two-dimensional (up-down combined with rotation) flapping wing that emulates biological capability. This work also supports the MAST program. Until this millimeter-scale mobility could be demonstrated, the “air” portion of the MAST program was nothing more than creative viewgraph engineering. In that sense, this effort has validated the MAST vision.
Another piezoMEMS project is investigating phase shifters as an element in the compact radar project. The work is on electronically scanned arrays, and the phase shifters have achieved 5 to 10 V activation, as compared with the 30 to 100 V achieved for others.
Both of these piezoMEMS projects emphasize the importance of the SEDD Semiconductor Fabrication Facility. The fabrication of piezoMEMS devices utilizes a unique process. It would very difficult, if not impossible, for SEDD to have this done at an outside fabrication facility, which could not customize its process, and whose processing delays would hamper the research substantially.
The radio-frequency prognostics and diagnostics for condition-based maintenance project has put together the correct set of comprehensive tools to solve an extremely important problem for the Army. The prognosis approach was particularly impressive, because it combined an intelligent choice of sensors with a layered set of complex algorithms for failure prediction.
The broadband digital waveform synthesis project has successfully achieved effective compensation for cross-talk errors generated when using multi-amplitude, multiphase modulation techniques such as quadrature amplitude modulation (QAM). The technique has been shown to compensate for transmitter nonlinearities for a 32-QAM system. The investigators predict that this method can increase the transmitter dynamic range by 20 dB.
In the Antennas and RF Technology Integration Branch, the compact millimeter-wave radar and advanced imaging project exploits a very clever idea of using stacked single antennas to get azimuth coverage quickly while minimizing complexity. It has also adopted a very interesting computational imaging system that is a hybrid of optical and radar approaches for a stepped-frequency, holographic radar imager. This combination has the potential to be a very interesting testbed that can link experimental data with new processing algorithms.
Highlights in the RF Signal Processing and Modeling Branch include the SIRE (Synchronous Impulse Reconstruction) Ultra Wideband Radar Program, which represents an excellent example of the SEDD research with the potential for a significant impact on the capabilities of a warfighter. It has multiple potential uses: (1) the detection of concealed obstacles behind foliage, (2) surface and buried mine detection for autonomously and nonautonomously operated vehicles, and (3) through-the-wall detection in an urban environment. The system is capable of many novel techniques, such as forward-looking synthetic aperture radar operation for determination of the height of obstacles, through-the-wall detection of moving people using noncoherent back projection, and change detection. It uses a very short pulse (~300 picoseconds [ps]), yet it employs a low-cost analog-to-digital converter. Its relatively low maximum frequency of operation of S band permits seeing through foliage and through building walls. Several challenges remain—in particular relating to real-time processing capabilities—but this is a high-payoff project with significant progress in the current review period.
Research in SEDD on the III-nitrides continues to be of the highest quality. The project carrying out this work showcases the expertise, exceptional instrumentation, and technical capabilities of SEDD, and it demonstrates the pivotal role that SEDD plays in the III-nitride community, serving as an impartial, highly respected evaluator that can knowledgeably assess materials from different laboratories, providing conclusions and comparisons that can influence the field to make improvements in materials. These insights also inform the research program internal to SEDD. Internal projects show great understanding of the important applications for the Army, and in general they also demonstrate sophistication in the understanding of materials and electronic structures, how best to engineer device structures, and how to characterize their behavior. SEDD has addressed important issues in high-efficiency deep ultraviolet devices and has made advances in the very critical droop in InGaN devices.
High-performance infrared sensors are an important application for the Army, and HgCdTe is a critical material to enable those sensors. Driven by issues of cost and performance for large-area detector arrays, SEDD has taken a leadership role in developing a composite substrate technology based on Si, carrying out fundamental studies in growth and processing to reduce defects arising from the lattice-mismatched growth of HgCdTe on those substrates, and establishing the correlation between defects
and device performance. SEDD researchers have amplified their efforts in this area by coordinating a network of small companies, larger companies, and universities to address comprehensively the issues of materials characterization, processing, device architecture, and array fabrication and characterization.
The SEDD project on dilute nitrides as an alternative, low-cost approach to achieving long-wave-length infrared (LWIR) detectors has incorporated some extremely clever and interesting ideas: lever-aging the use of nuclear resonance analysis (used to study gun barrel erosion) to sensitively map out N concentrations and locations, and using transmutation doping to achieve p-type doping in the material. The ability to construct an LWIR detector from III-V materials is extremely important for the Army. This work is impressive because a newer material, InAsSbN, has been selected, and a technique for growing it in a lattice-matched condition has been demonstrated.
The SEDD effort on polarization properties of nitride semiconductors has achieved a key break-through in the fabrication of a GaN single-heterostructure light-emitting diode (LED) with the p-side down. By placing the p doped side on the substrate, a potential barrier is introduced that limits the electron overshoot into the p-GaN layer. The results show a factor-of-five reduction in efficiency droop over conventional GaN LEDs at high current density (>100 A/cm2). This new structure also offers a real chance to make a high-efficiency solid-state ultraviolet laser.
Working in coordination with the Flexible Display Center in Arizona, SEDD has become the leader in flexible display technology and is stimulating the industry. The Flexible Display Center appears to be bearing fruit, and industry is participating and contributing technology.
SEDD efforts in biotechnology have established or enhanced ARL expertise in this area of importance to the Army. Investigators appear to have an excellent understanding of the opportunities and limitations of the science, the instrumentation, and the Army-related applications. Two efforts of note are the Affinity Reagent Isolation for Pathogen Detection and the Cell-Based Sensing projects.
Signal processing is fundamentally a systems technology in which algorithms are developed to solve key systems needs. Superb results are achieved when those developing such algorithms have the advantage of a deep understanding of the problem. High-quality work benefits enormously from direct exposure to the real problem and real data. The RF Signal Processing and Modeling Branch has a track record of outstanding work in this area, with its deep involvement with technology now in use in Iraq and Afghanistan.
A good example of a high-value outcome from this branch is the Acoustic Signal Localization and Classification project. The goal is the use of acoustic sensors to detect an explosion or firing location with sufficient accuracy to cue a sensor or response. Unfortunately, spatial- and time-varying temperature and wind gradients both change the direction of arrival of the signal and, through multipath, distort it. This distortion puts limits on how such sensors can be used. Getting more value from acoustic sensors by removing this distortion is a very hard problem that is now being examined at ARL. There has been a great deal of work over many years aimed at modeling these effects with sufficient accuracy to permit compensating for the effects by processing. With a great deal of expertise, SEDD continues to develop a model to help address this problem.
The current focus of SEDD efforts in sensor and information fusion for coalition networks is authentication and sensor-network-access permissions, which are of great practical importance for deploying among coalition forces a system used in a hostile environment. This work is set against a backdrop of more general fusion processing that must effectively integrate information from sensors with very different types of information in terms of kind, quality, and timeliness. The project team has properly identified the need to address fusion in the context of real data from specific sensors. Such a system is very likely to be of greater value than sensor information that is fused at a tactical level only and then fed forward.
One of the image-processing efforts associated with the SIRE radar is the Through-the-Wall Detection of Moving Personnel project. It is focused on detecting through walls the number and location of individuals within a structure. The current effort has a good processing architecture, with the individual components well executed. The processing now is largely addressing the problem of finding the interesting signal associated with moving personnel amid other returns. The current results are separated from the background by exploiting the regular movement of simulated persons. This is a good first step, with ongoing efforts focused on the kind of movement that can be expected of persons in realistic scenarios.
OPPORTUNITIES AND CHALLENGES
SEDD researchers have demonstrated significant cleverness in solving problems faced by the Army. Cleverness of approach can be as important a metric as standard academic measures (e.g., journal publication) for judging quality of science. This section lists a number of specific opportunities for investigators within SEDD and outlines some of the particular challenges being addressed by SEDD staff.
Micropower is an especially promising area that, with the application of adequate resources, could produce outstanding results that could be transitioned ultimately to fieldable technologies. This area is particularly important because of its impact on many of the projects that fall under SEDD’s interest areas.
The SiC area represents a success for SEDD. This has been a long-standing area of investment owing due to the Army’s need for high-power switching components. This effort is unique and very appropriate to ARL’s niche. Partly as a result of this investment, SiC metal-oxide semiconductor devices are now being commercially offered by two vendors, Cree and General Electric. SEDD’s role is now evolving but should not be eliminated. The new mission is to take part in the reliability evaluation and the setting of standards for the industry. As SiC is transitioning to a more commercial technology, SEDD can explore the possibilities of the III-nitrides as switches. Development of the III-nitride switching devices is a very long term materials-based effort. As is the case with SiC, few other organizations can be patient enough to provide the long-term support to solve the materials issues. SEDD is in a unique place in this arena.
Fuel cell research within SEDD is making progress. The researchers are active in the community and are publishing. JP-8 reforming is an excellent strategic area that should be developed by SEDD. There is a clear need from the Department of Defense for this technology and no strong commercial driver for it. This is an area in which SEDD could make significant impact. That being said, it is also a long and difficult road that will require sustained and disciplined work.
Strategic investments in materials technologies can have broad applicability throughout the divisions in SEDD. For example, the wide bandgap materials influence the Radio Frequency and Electronics Division’s work in GaN power electronics, the Electro-Optics and Photonics Division’s work in deep ultraviolet optoelectronics, and the Energy and Power Generation Division’s work in SiC electronics. Within a given division, there may be a range of technology choices that can be explored. Where there are common applications that can be met by competitive technologies (e.g., power switching through wide bandgap electronic devices: SiC versus GaN), it is important to carry out periodic internal benchmarking and comparison to avoid redundant efforts and to make the best use of limited resources.
The staff in the life sciences at ARL have developed a more sophisticated understanding of Army needs, are immersed in meaningful collaborations with organizations both intramural (other ARL directorates) and extramural (e.g., the Institute for Collaborative Biotechnologies), are making
reasonable progress establishing life science experimental capabilities, and are starting to develop focus areas. That said, ARL and SEDD management have some significant and difficult focus decisions to make in the next few years. More application-driven advice from senior life scientists (rare people to find outside of industry) is needed to help management with the decisions as well as the later stages of the current projects.
In signal processing there is a “clear and present overload” of data coming from the imaging sensors that are being used with great success throughout hostile regions. The huge data sets generated exceed the capacity of tactical communications links. As a result, data that must be analyzed often take too long to get into the right hands and consequently do not achieve the impact that they should. A very high payoff can result from technical work in the area of automated tactical alerts designed to flag and prioritize data that should be urgently transmitted over the limited communications links available. Such an effort should be explicitly constrained to run on hardware with limited power and weight. Through its processing expertise and classified programs, ARL is in a unique position to make such a contribution.
The SEDD Semiconductor Fabrication Facility has again proven to be a success story for enhancing research at ARL. As discussed in the previous ARLTAB review of SEDD activities, the Semiconductor Fabrication Facility is a magnet for early-career researchers and has aided in their recruiting. In addition, it has fostered collaborative research with other organizations, acting as a technical force multiplier. The technical difficulties in managing a semiconductor facility that supports so many types of processing are greatly increased over those in a facility that supports only one type of processing—for example, complementary metal-oxide semiconductor or GaAs. Issues abound over the use of common equipment with potential cross-contamination and the maintenance of tight process control with the different process lines. In this regard, only a few top-ranked universities have achieved a high performance level, but SEDD has also mastered it. ARL has done well to continue its investment in the maintenance and modernization of this facility and must be prepared for the significant investments necessary to keep this facility equipped with state-of-the-art technology.
OVERALL TECHNICAL QUALITY OF THE WORK
The scientific quality of the research at SEDD is of comparable technical quality to that executed in leading federal, university, and/or industrial laboratories both nationally and internationally. The balance between work on projects with immediate applications to the war zone, such as the detection of improvised explosive devices, versus basic research work, such as that on the cold atoms, is very good. There is also evident an impressive level of the involvement of other agencies and civilian industry in the ARL projects both as collaborators and as customers.
Measured by refereed publications and citations, SEDD is doing very well. According to the data supplied to the panel for the 18-month period from January 2009 to June 2010, SEDD staff published 136 refereed journal papers and presented 522 papers at conferences and symposia. Of the presentations, several are invited and international—for example, by the 50th Battery Symposium in Japan. Several papers on fuel cells and batteries were presented at the Electrochemical Society meeting in 2008 in Honolulu, which is impressive. Based on the data provided, the average publication rate for individual SEDD staff is comparable to the averages of university-based researchers and slightly better than those of most industrial laboratories. The publications are in good-quality journals and at top-tier conferences. In FY 2009, 20 patents were awarded to SEDD researchers, and 27 new applications were filed. This is a track record of a solid research organization.
There are several crown jewel projects in which SEDD researchers are leading the field. Most notable is the work in quantum detectors and III-nitride materials for sources and detectors. SEDD’s leadership in this field stems not just from its top-notch scientific staff but also from the world-class fabrication facilities that it maintains. Another area of SEDD leadership is in acoustic processing and electromagnetic field sensing. SEDD researchers in this area can point to immediate impacts on the battlefield: several systems from this group have been deployed in recent years. Semiconductor power switching and conditioning devices are also an area of leadership. This results from a combination of quality staff, excellent facilities, and a direct application to Army requirements. Although its participation in the Flexible Display Center is not an internal program, it is important to note the role that SEDD plays in the center. Flexible display technology promises potentially extensive consumer and military applications. However, in some specifications, devices for these two markets may not coincide. The participation of SEDD in this center, generally to assist in the advancement of the technology, but additionally to see that military needs are met, shows significant foresight by ARL and SEDD management.
In general, the quality, enthusiasm, and morale of SEDD staff are excellent. Such indicators of the scientific culture of an organization can be as important as quantitative measures such as papers, citations, and patents for assessing the quality of the science. Interactions among enthusiastic colleagues lie at the forefront of scientific advances, because often ideas are sparked during both formal and informal conversations with colleagues. SEDD is clearly fertile ground for such interactions.