Larry P. Sadwick

Effect of exponentially graded base doping on the performance of GaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5*10/sup 19/ cm/sup -3/ at the emitter edge to 5*10/sup 18/ cm/sup -3/ at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1*10/sup 19/ cm/sup -3/, the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%.<<ETX>>

A new improved slow wave structure for broadband millimeter wave traveling wave tubes

There continues to be increasing demands for high performance broadband traveling wave tubes (TWTs) at millimeter waves (MMW) for communications applications. The high performance requirements for these TWTs include relatively high power, efficiency, and good linearity. The smaller size and the associated effects of the small size on the manufacture of these MMW TWTs, together with the relatively high power requirements, provide motivation for innovative improvements in slow wave structures (SWSs) for high performance, high power MMW TWTs.

Ku band, 100 kW traveling wave tube based on large quasi-optical spatial power combining array

We report here further development of the novel quasi-optical spatial power combining array for high power millimeter wave (MMW) traveling wave tubes (TWTs) by demonstrating a Ku-band high power TWT which covers 12-15 GHz and with 100 kilowatt (kW) output power. Specifically, a Ku-band high power TWT which consists of a quasi-optical spatial power combining array of fifteen beam-wave interaction circuit slow wave structures and, as a result, beam width/height aspect ratio of close to 85 was developed to achieve a combined output power of over 100 kW at Ku-band. The 15 individual beam-wave interaction structures in the quasi-optical spatial power combining array are arranged into a linear array. Instead of a single cathode, fifteen cathodes, each with its own focus electrode or, in other words, a total of 15 focus electrodes are also used to create a required large sheet of beam for the large quasi-optical spatial power combining array of 15 channels of individual beam-wave interaction structure. Although a single stage collector was initially designed, however, a multi-stage depressed collector will also be designed and implemented to improve the efficiency of this K-band high power TWT. The overall size of the Ku-band high power TWT is relatively small since the same vacuum envelope and electron beam focus optics are shared among the five beam-wave interaction structures. Design and fabrication of this Ku-band high power TWT will be presented to demonstrate the large quasi optical spatial power combining array for very high power MMW TWTs and with reasonable broad bandwidth.

High‐temperature, radiation‐hard electronic technology

We report on two novel high temperature and potentially highly neutron and gamma radiation resistant electronc technologies that are suitable for nuclear and space applications. The operational effects on these technologies from gamma radiation doses up to 10 megarads and 1‐MeV equivalent neutron fluences up to 1014 neutrons/cm2 are examined using a calibrated (to appropriate ASTM standards) irradiation chamber in the University of Utah TRIGA Nuclear Reactor. The first high temperature, harsh environment technology is based on microminiature vacuum (MTV) devices. The second high temperature technology is gallium arsenide (GaAs) metal semiconductor field effect transistor (MESFET)‐based devices and circuits that can operate at temperatures up to 350 °C. This MESFET‐based technology also allows a wide range of control with respect to the MESFET’s enhanced resistance to breakdown at elevated temperatures. The MESFET‐based technology has general applicability and works equally well with both enhancement and d...

Progress in microminiature thermionic vacuum tube devices

We report on the progress made in the fabrication and testing of microminiature thermionic vacuum (MTV) tube devices with ultra-small (i.e., micron-scale) dimensions. In particular, using low function material, we have been able to successfully fabricate reproducible and reliable MTV planar and vertical diodes with emission properties that obey Childs Law for emission distances on the scale of approximately 2 /spl mu/m or greater. MTV technology is well suited for use in flat panel displays, electron beam writing sources and optics, nuclear instrumentation, aeronautical control instrumentation, space-based missions, geothermal and oil exploration, and other high temperature and harsh environment applications.<<ETX>>

Microminiature thermionic vacuum tube diodes

Details on the fabrication and testing of microminiature thermionic vacuum tube devices (i.e., diodes, triodes) with ultra-small (i.e., micron-scale) dimensions will be presented. The microminiature thermionic vacuum (MTV) devices can either have a direct or indirect heated cathode with an air-bridge filament supplying the thermal energy. Single device element architecture can consist of either a totally vertical structure or a combination of planar and vertical structures. The MTV devices are well suited to harsh environments and have the potential to operate at frequencies approaching the terahertz range.<<ETX>>

A comparison of commercially available quasistatic meters and methods

The capacitance-voltage (C-V) technique is one of the most powerful and direct methods to investigate interface traps in metal-insulator-semiconductor (MIS or MOS) related devices. As the C-V technique is of such fundamental importance in detecting and monitoring process related defects the systematic measurement concerns, misinterpretations and limitations associated with the equipment used to implement this technique must be fully understood and characterized. This study reports the results of a detailed comparison of both the (raw) measured C-V curve and the (analyzed) interface trap density versus energy data obtained using commercially available quasistatic meters, specifically the Hewlett-Packard (HP) model 4140B quasistatic/dc picoammeter and the Keithley model 595 quasistatic meter.

3D printing additive manufacturing of W-band vacuum tube parts

InnoSys is developing 3D printing additive manufacturing suitable for reliable production of microwave and millimeter wave Vacuum Electronic Devices (VEDs) or, specifically, traveling wave tubes (TWTs). 3D printing additive manufacturing enables direct-from-CAD manufacturing and will revolutionize VED making compared to the limitations faced by conventional manufacturing for high-precision and laboring assembly alignment. Additive manufacturing also provides faster and lower cost replacement parts and devices for existing tubes. This initial work has demonstrated that new materials and material processing associated with 3D printing suitable to replace existing vacuum-grade and vacuum tube compatible materials can be achieved. The ability to produce parts as needed and reduce the waste of expensive materials would be a boon to the industry. Although only at the beginning of our efforts, we have achieved the initial objective of demonstrating that 3D printing additive manufacturing could be developed for microwave and millimeter wave VED manufacturing with much improved flexibility and cost reduction. This was accomplished through the associated material and processing alternatives with 3D printing suitable for microwave and millimeter wave vacuum tube production that can meet or possibly in the future exceed the performance and reliability of existing materials and processes while significantly decreasing the cost, time, manual labor of fabricating components and assembling, for example, microwave tubes.

Quasi-optical spatial power combining millimeter wave high power traveling wave tubes

A quasi optical spatial power combining traveling wave tube has been successfully developed and used to increase the output power from solid state devices (as the driver). We report here the development of novel quasi optical spatial power combining for vacuum electronic devices and, more specifically, for traveling wave tubes (TWTs) to increase output power at millimeter waves (MMW) and higher frequencies. A quasi optical spatial power combining array of five complete plus two half slow wave structures (SWSs) was developed at W-band (center frequency 95 GHz) to achieve a combined output power of over 1000 Watts. These SWSs are arranged into a linear array. A sheet beam electron gun and a single stage collector were designed and implemented to mate to the SWSs for this W-band high power TWT.

Electromagnetic analysis of external cavity design for high power semiconductor lasers

To achieve high power single mode output from an edge emitting semiconductor laser diode, we made an approach to use external cavities to improve the beam quality by providing optical feedback into the laser. By performing both simulation and experiments, we have found out that the external cavity works well to generate single mode laser beams.