This paper extends a methodology for microelectronics verification to the situation in which signal switches are applied to library circuits containing INV, NAND2, NOR2, NAND3, and NOR3 gates. Monte Carlo methods are used to sample the frequency distributions of the topological genus of library circuits including a 4-bit adder.

It has long been recognized in the design of micromirror-based optical systems that balancing static flatness of the mirror surface through structural design with the system's mechanical dynamic response is challenging. Although a variety of mass reduction approaches have been presented in the literature to address this performance trade, there has been little quantifiable comparison reported. In this work, different mass reduction approaches, some unique to the work, are quantifiably compared with solid plate thinning in both curvature and mass using commercial finite element simulation of a specific square silicon-on-insulator-based micromirror geometry. Other important considerations for micromirror surfaces, including surface profile and smoothness, are also discussed. Fabrication of one of these geometries, a two-dimensional tessellated square pattern, was performed in the presence of a 400-mu m-tall central post structure using a simple single mask process. Limited experimental curvature measurements of fabricated samples are shown to correspond well with properly characterized simulation results and indicate similar to 67% improvement in radius of curvature in comparison to a solid plate design of equivalent mass. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Successful integration of linear-mode photoconductive semiconductor switches (PCSS) into RF pulsing antenna sources may yield higher switching speeds and improved power efficiency over conventional switching methods, while also reducing size/weight. This paper presents a multiphysics computational methodology for studying linear-mode PCSS in a high-power antenna system, with a focus on extrinsically triggered wide-bandgap materials. A comparison with the existing literature reveals crucial performance sensitivities to photon absorption models, as well as encouraging results for the potential of PCSS as high-power switching devices.

The integration of photoconductive semiconductor switches (PCSSs) into pulsed power systems may have improvements over conventional switching, but failure modes occurring near the illuminated edge of PCSS devices between switching operations present a serious limiting factor. While these failure modes have previously been difficult to characterize, this paper proposes a theory for a potential contributing source of failure supported by observations derived from the results of an FDTD simulation on an optically excited semiconductor switch. A computational analysis combining both solid-state and electromagnetic physical models reveals what appears to be an unintentional waveguide-like behavior in the optically excited plasma-filled PCSS device in strong agreement with the documented observations in the experiment. The net effect of nonuniform charge carrier generation as a result of waveguide-like mode formation is theoretically assessed, and the additional areas of investigation into this pivotal problem area in the PCSS design are suggested.

Silicon-based micromachining techniques were investigated as a method of encapsulating electronics in thin-walled spheroidal shells. Various bulk isotropic etching methods were utilized to produce hemispherical cavities in silicon wafers. sulfur hexafluoride (SF6) based plasma was determined to be a preferable alternative to wet HNA etching when performing repeatable isotropic etches in silicon. Silicon crystal orientation’s effect on etch variance and anisotropy was also investigated. HNA polishing was demonstrated as an effective method of reducing undercutting, surface roughness, and anisotropy. Image processing routines were developed and incorporated into etch analysis, improving data collection efficiency. These hemispherical silicon cavities serve as a template for thin film deposition of a hemispherical shell, or hemishell. Photoresist can be patterned over the hemishells with 3D photolithography techniques, facilitating the deposition of metal traces and bonding sites. To improve throughput, a novel closed-loop photolithography technique was developed. This technique leverages the capabilities of existing cleanroom devices to perform precise alignment and patterning. After patterning, hemishells can be aligned and bonded using modern packaging technologies, and separated from the silicon wafers using selective etch chemistries. The 0.1–1 mm3, spheroidal structures present an innovative packaging alternative for a wide variety of microdevices. Particular applications include electrostatically actuated microrobots and non-invasive ubiquitous microsensors.

This paper presents topological constraints of gate-level circuits obtained through standard cell recognition applied to gate-level commercial microelectronics verification. A suite of topological constraints, including the gate vertex count, net vertex count, terminal count, blocks, circuit genus, Euler characteristic, and number of faces are extracted from gate-level circuits obtained through standard cell recognition. Topological constraints are computed for two full adder cells at fourth level of abstraction and for two full adder cells at the third level of abstraction. Two mathematical frameworks are also introduced to describe physically distinct situations in hardware that are represented in a schematic as functionally equivalent. The first method uses the concept of a braid word, and the second method uses the concept of a crossing vertex. Schematic braid words corresponding to each of two full adder cell schematics at fourth level of abstraction and for two full adder cell schematics at the third level of abstraction are derived. Chip braid words corresponding to the set of unique physical designs that could potentially be realized in chip hardware from a schematic are obtained and discussed. Potential capabilities of these approaches for gate-level circuits are discussed.

Fig 2 shows a cross sectional SEM image of the channel area after etching tungsten prior to stripping the PMMA etch mask. The thickness of the ZnO film measured ∼52 nm, both in the channel area and underneath the source/drain pads, indicating that the ZnO film was not thinned during the plasma-etch process. Fig 3(a) and (b) show the I D -V D output characteristics of a ZnO TFT with a 155 nm and 425 nm channel, respectively. The maximum observed drain current density (I D ) and transconductance (g m ) for the 155 nm devices was 830 mA/mm and 121 mS/mm, respectively. However, the devices do not saturate at high V D values, due to lateral breakdown limitations of the short channels. Fig 3(c) shows I D plotted as a function of V G on both a log- and linear-scale for devices operating in the linear region with measured channel lengths of 155, 215, 325 and 425 nm. The devices show a near linear dependence on I D versus L C . However, a negative shift in the on-voltage (V on ), defined as the gate voltage when I D begins its initial increase the log(I D )-V G plot [4] is observed as L C is decreased. Fig 4(a) shows the extracted on-resistance (R on ) plotted as a function of channel length. From the data, the total parasitic source/drain resistance (R SD ) can be extracted by gated-TLM method [5], shown in Fig 4(b). The devices exhibit a width normalized R SD of 2.1 Ω·mm indicating the tungsten/ZnO interface resistance is low.

Increasing Student and Faculty Participation in an Undergraduate STEM Summer Research Program in a Government Institution through a Higher Education PartnershipAbstractThis paper describes steps taken to increase participation in an undergraduate STEM SummerResearch Program at the Air Force Institute of Technology (AFIT), a government institution.These steps are taken during the third year of an ongoing process to transform the undergraduateprogram. A partnership among AFIT, the LEADER (Launching Equity in the Academy acrossthe Dayton Entrepreneurial Region) Consortium, and the Southwestern Ohio Consortium forHigher Education (SOCHE) was established to assess the students’ experiences and to informfuture experiences based upon the results of surveys conducted annually since 2012. SOCHEhas employed nearly 1,000 STEM students in the past 25 years.In 2012, a formal assessment tool was distributed to the students for the first time to measure theimpact of the research experience. Also in 2012, a formal assessment tool was distributed to theFaculty Advisors of the students for the first time to measure the research experience of thestudents from their advisors’ perspective. Following the student survey results in the 2012Program, we identified the following four broad needs expressed by the students: (1) A desire formentors with increased organization and communication among SOCHE, AFIT, and thestudents; (2) A desire for increased interactions with other students; (3) A desire to improve theirCV or resume at the beginning of the program; (4) A desire to gain engineering experience,skills, and confidence in research.In the 2013 Program, we introduced and implemented four new voluntary components inresponse to the student needs. Because of government restrictions, the participation of students inthe components is voluntary, and students were encouraged to participate by SOCHE. Thesetransformational components are: (A) A joint orientation process with SOCHE and AFIT ProjectLeaders; (B) Student cohorts through social activities and STEM-based games; (C) A weeklyseminar meeting with outside presentations of general interest; and (D) A Poster Session so thatstudents can present the engineering experiences they have gained. Selected students wereawarded “Posters of Excellence” Certificates in a poster competition.Student response rates in the 2013 Program were low to both a pre-survey administered bySOCHE when the program was in session and to a post-survey following the program (pre-survey response rate: 33%; post-survey response rate: 16%). While participation in the JointOrientation was nearly 100%, student participation in the other 11 one-hour weekly events waslow (13%).This paper describes increased student and faculty participation in the 2014 Program. The 2014Program comprised 50 students and 14 Faculty Advisors. The 50 participating students is thelargest number of students since the start of our assessment effort (The 2013 Program comprised43 students, and the 2012 Program comprised 48 students). SOCHE continues to advertise theresearch internships conducted at the Federal Government Institution throughout southwesternOhio.In the 2014 Program, we introduced and implemented a fifth component. This component is: (E)Counseling. This component provides personal interaction among the students and SOCHE atthe Government Institution (where the students are pursuing their research projects). In thiscomponent, the Director of SOCHE drove to the Government Institution for one day(Wednesday) each week and spent four hours meeting informally with students and answeringstudent questions regarding the Program. Approximately 20 students met the Director each day.In addition to introducing Component (E), we also standardized the location and time of eachevent in the four components (A)-(D). Each event was held at the same time (noon-1pm) eachweek in the same location. The consistency of the programming helped the students remembereach weekly event and contributed to increased participation.This paper will describe the new component (E) and additional steps taken to increase studentparticipation in the five components in the 2014 Program. This paper will also describe stepstaken to increase faculty participation in the Faculty Advisor survey.In the 2014 Program, student participation increased in each component. Nearly 100% of thestudents participated in the Joint Orientation. Thirteen of the 50 students (26%) participated inthe Kayak trip; 18 students (36%) participated in the resume workshop; and 21 students (42%)participated in the Poster Preparation Session. Seventeen students (34%) prepared 12 posters forthe Poster Session, compared with the participation of 9 out of 43 students (21%) who togetherprepared 7 posters in the 2013 Poster Session (a Poster Session was not held in the 2012Program). Faculty participation in the 2014 Faculty Advisor survey is 11 out of 13 on-campusfaculty (85%) (One faculty transferred out of the country prior to the administration of theFaculty Advisor Survey and was not able to be surveyed). The increased faculty participationrate in the 2014 Program compares favorably to the Faculty Advisor response rate of 56% in the2013 Program and 61% in the 2012 Program.Our capability to strengthen the program focuses on incorporating feedback from the students,who are government contractors, and incorporating feedback from the Faculty Advisors in orderto inform best practices in workforce development. Additional results and findings of theassessment of the 2014 Summer Research Program will be discussed, and the results andfindings will be compared with results from the 2012 Program and 2013 Program.

UWBSP EM systems typically rely on spark gap or vacuum tube-based devices because of the significant current and voltage magnitudes involved. Historically, solid-state devices have not been able to resist dielectric breakdown and the subsequent catastrophic failure modes that result in device damage when the large, pulsed bias voltages associated with UWBSP applications are applied. Recent advances in semi-insulating WBG materials have the potential to create switches that relieve the breakdown problem, while also allowing for more predictable, controllable, stable, and efficient switching at a reduced size and weight than what has been possible with traditional high power switching technologies. These WBG switches are operated by virtue of optical excitation of charge carriers from dopants deep within the band gap, also known as extrinsic photoconduction. This paper presents a hybrid computational approach for investigating a PCSS-based UWBSP system, focusing on the source and accompanying antenna radiation. The PCSS is simulated through Synopsys Sentaurus, using an array of fundamental and user-defined solid-state physics models. Both conventional and WBG materials are examined, and compared to published data in existing literature on comparable spark gap and PCSS systems. The results of the PCSS are used to excite two lossy UWB antenna designs, and the radiated output signals are compared both to each other and to existing literature. The results indicate that PCSS possess very high potential for not only matching but also exceeding the performance of spark gap based devices. The thick dipole UWB antenna appears to be a better suited design for radiating the transient signal switched by the PCSS than the bow tie antenna, with a higher amplitude of radiated power and far electric field. The magnitude of the radiation presents a compelling case for further investigation into the prospect of further developing solid-state driving sources for high power electromagnetic radiating systems. More advanced material measurement and characterization of the physical process involved with critical aspects of the switch, such as extrinsic photoconduction, are required in order to produce a higher fidelity model for future research.

The integration of optoelectronic devices, such as photoconductive semiconductor switches (PCSS), into existing antenna source architectures for the generation of radio frequency (RF) pulses may yield higher switching speeds and improved power efficiency over conventional switching methods while reducing size/weight. The key enabling technologies for this design include semi-insulating wide bandgap materials and extrinsic photoconduction: Both of which involve physical models that still require further investigation. This paper presents a computational methodology for studying a novel PCSS design based on existing data through the use of multiple integrated solvers for each major physical domain. In addition, it presents a comparison to current literature on modern conventional and optical switching systems for pulsed radiating systems.

This paper describes first steps to transform all internships in the undergraduate STEM Summer Research Program in the federal government at the Air Force Institute of Technology (AFIT) to prepare students for engineering careers in the 21st century. AFIT is a government institution of higher education within the Air Force. Over 40 students participate annually and perform research in all six engineering departments at the AFIT Graduate School of Engineering and Management. These are the departments of Aeronautics and Astronautics, Electrical and Computer Engineering, Engineering Physics, Mathematics and Statistics, Operational Sciences, and Systems Engineering and Management.First, starting in summer 2012, a formal assessment tool is now distributed to students to measure the impact of the research experience. Second, starting in summer 2013, students are now provided with four career broadening programs that are informed by student survey results in 2012. These programs are made possible through a partnership among AFIT, the LEADER (Launching Equity in the Academy across the Dayton Entrepreneurial Region) Consortium, and the Southwestern Ohio Consortium for Higher Education (SOCHE). The partnership assesses the students' experiences and informs future experiences based upon the results of student surveys. SOCHE has employed nearly 1,000 STEM students in the past 25 years.Feedback was sought in 2012 from the 48 participating students to improve all internships in the Summer Research Program in order to help prepare engineering student interns for work in the 21st century. In response to the feedback, four new voluntary program components were made available to all students in the 2013 Program. Because of government restrictions, student participation is voluntary. The components are: (A) A joint orientation process with SOCHE and AFIT Project Leaders; (B) Student cohorts through social activities and STEM-based games; (C) A weekly seminar meeting with outside presentations of general interest, such as job-hunting, resume-writing, information about scholarships and fellowships, and the process to apply to graduate school; and (D) A Poster Session so that students present the engineering experiences they have gained. A poster competition was held to select the best student posters, and selected students were awarded "Posters of Excellence" Certificates.In 2013, SOCHE again implemented an assessment tool in an effort to better understand the needs of the 43 participating students. Of these students, 10 students had also participated in the 2012 program (repeat participation rate of nearly 25%). SOCHE asked all 43 students to complete a pre survey when the program was in session (response rate: 33%) and a post survey following the program (response rate: 16%). Post survey responses are favorable to the career broadening programs. Student participation in the 12 one-hour weekly events was nearly 100% in the joint orientation and 13% in the other events.This paper will describe the importance of the four new career-broadening components to transform the internships at AFIT to prepare students for engineering careers in the 21st century. Additional results and findings of the assessment of the 2013 Summer Research Program will be discussed, and the results and findings will be compared with results from the 2012 Program.

Metamaterials offer custom electromagnetic properties not easily found elsewhere. In this investigation, we look at fabrication methods to reduce time and cost for metamaterials. These designs are compared against analytical modeling, and verified with experimental radio frequency (RF) testing. This paper discusses two models used to represent meta-atoms as lumped circuit elements to establish a resonant frequency. The analytic model is compared with a finite element method (FEM) modeling simulation to determine the capacitance and inductance of the meta-atom and establish a resonant frequency for the comparison. These modeling methods help to determine the resonant frequency before it can be experimentally verified. In this research, we experimentally show the resonant response at 2.57 GHz. In addition, various Metamaterial configurations are tested to capture effects for focusing and blocking electromagnetic waves. The best focusing response occurred at 2.57 GHz with a null of −21 dB with silver inkjet printed meta-atoms supported with FR4 material. The best blocking response occurred at 2.76 GHz with a null of −92 dB with silver inkjet printed meta-atoms supported with FR4 material. The experimental measurements provide characterization for the resonant response, and extraction of electromagnetic material properties which enhances the fundamental understanding for metamaterials.

The effects of bending a 2-dimensional planar array of rectangular split-ring resonators (SRRs) is observed by mounting the array to varying diameter HDPE cylinders. By studying the transmission of pulsed THz light through the SRR-cylinder system, it shown that the resonant frequency and response of the arrays are tunable as a function of the radius of curvature.

This paper presents an analysis of an inexact N-bit ripple carry adder architecture. Results show that a 30 percent power reduction is achieved for several approximate adders while maintaining a root-mean square error of 16 percent.

Microelectromechanical systems (MEMS) switch reliability is a major obstacle for large-volume commercial applications despite offering lower power consumption, better isolation, and lower insertion loss compared to conventional field-effect transistors and PIN diodes (Yang et al. IEEE J Microelectromech Syst 18(2): 287–295, 2009). To enhance reliability and performance, MEMS researchers focus on the micro-contact lifecycle evolution based on material choice and design of the micro-contact. In order to examine the micro-contact phenomena and physics, a novel DC MEMS micro-contact structure has been developed. The structure is composed of a Gold contact pad and a layered Gold beam. The reliability and performance of a micro-contact is directly influenced by its ability to make and break its electrical connection. Its ability to separate from the contact area is a function of applied force, adhesion forces, and the restoring force. The layered Gold micro-contact structure was fabricated and the processing steps, performance, and experimental results of the device reliability of the device are presented.

Frequency selective surfaces are being used in applications from RF to optical systems. Current applications involve beam steering or blocking transmission for electromagnetic signals. The RF Meta-atom is an excellent and novel component for frequency selective surfaces which alter or block propagating RF signals. Based on research into the tunable RF meta-atoms, a frequency selective surface has been developed that effects the propagation of RF signals. Integrating RF meta-atoms with microelectromechanical systems varactors provides a tunable method for frequency selective surfaces. Optimization of the frequency selective surface is performed through design, modeling, simulation and experimental testing for controlling propagating electromagnetic signals. To test the design concept, an RF meta-atom array was fabricated using surface micromachining fabrication methods. The RF meta-atom array was placed into RF strip-line to experimentally show the transmission and reflection response of propagating electromagnetic signals impending onto the array. The experimental results show that the resonant null at 4.85 GHz decreases from a transmission magnitude of 0.51 at 0 VDC to 0.14 at 70 VDC. This investigation shows results on how RF meta-atoms integrated with MEMS varactors can be arrayed for frequency selective surfaces.

Films subsumed with topological defects are transformed into complex, topographical surface features with light irradiation of azobenzene-functionalized liquid crystal polymer networks (azo-LCNs). Using a specially designed optical setup and photoalignment materials, azo-LCN films containing either singular or multiple defects with strengths ranging from |½| to as much as |10| are examined. The local order of an azo-LCN material for a given defect strength dictates a complex, mechanical response observed as topographical surface features.

This paper introduces a novel and unique paradigm to upgrade a long-standing summer research program at a government institution to include components that are now standard at civilian programs, such as National Science Foundation (NSF) Research Experiences for Undergraduates (REU) programs. Critical to the success of this new paradigm is a campus-community partnership. This partnership makes it possible for the first time to assess the summer program at the government institution due to government regulations. The AFIT Summer Research Program hosts approximately 50 student contractors each summer; making the program four to five times larger than a typical NSF REU program, and over 10% are female. All students who participate in the AFIT Summer Research Program are required to be U.S. citizens, and are employed under a contractor through the Southwestern Ohio Council for Higher Education (SOCHE). SOCHE has employed nearly 1,000 STEM students over the past 25 years in both summer programs and year-long programs. During this time, a formal assessment tool was not distributed to students to measure the impact of the research experience on student learning because federal regulations [AFI38-501] do not permit Air Force employees at AFIT to legally survey the students since the students work in contractor status (Air Force employees are not legally permitted to survey contractors in any form; neither paper surveys or email surveys are permitted). Due to AFIT policies and procedures surrounding contractors, the AFIT Summer Research Program lacks components of standard comparable NSF-funded REU programs summer research programs at other institutions. These regulations include not being legally permitted to buy refreshments for informal student cohort meetings, not having a dedicated program coordinator, not offering group meetings to discuss resumes, careers, graduate school, or offer a poster conference. While it is typical at other NSF-funded REU programs to have a program coordinator, each student in the AFIT Summer Research Program is directed through his or her own AFIT Faculty Advisor and has a unique experience. Another unique aspect of the AFIT summer program is that all students are required to work the same core hours between 0900 and 1500 each day. The new

Light can induce rich and diverse topographical transformations of initially flat films composed of photoresponsive, azobenzene-functionalized liquid-crystalline polymer networks. The N-fold symmetry of the topography of the photoinduced response of defect-containing azo-LCN films is examined by T. J. White and co-workers on page 5880. It is found to be inherently coupled to the strength of the defect, confirming that the director profile emanating from the topological defect governs the behavior. The topography of a film subsumed with a +10 defect resting on water after exposure to light is shown here.