Facilities

The Microwave/Millimeter Wave Laboratory is employed for both teaching and research activities. On the teaching side, students learn passive and active RF and microwave device analysis, and the design, fabrication, and testing of RF and microwave filters and circuits. In the course of their studies, the students also learn how to operate state-of-the-art microwave equipment (see Fig. 3) courtesy of generous donations from Agilent Technologies (now Keysight Technologies). A compact, 15 ft. long computerized, anechoic chamber (see Fig. 4) is available for both teaching and research use for antenna pattern testing at microwave (≤ 40 GHz) and millimeter-wave frequencies (40-220 GHz and above). The primary plasma diagnostics research in this facility has been directed toward imaging array development, quasi-optical beam splitter and notch filter arrays, and the use of phased antenna arrays for beam steering and beam focusing/defocusing applications for imaging reflectometry.

Fig. 3. Photographs of the teaching (left) and research (right) portions of the Microwave/ Millimeter-Wave Laboratory (3182 Kemper Hall).

The plasma diagnostics development work and testing as well as THz vacuum electronics R&D is carried out in Prof. Luhmann’s newly outfitted 12,000 ASF Spafford Road Laboratory facility (see Figs. 8-10 below) housing some of the Davis Millimeter Wave Research Center (DMRC) millimeter wave and THz facilities. This is located only 2.4 miles from the main campus (see building figures below). The state-of-the-art facility (Figure 9) houses a cleanroom, a chemistry room with three fume hoods, and six high temperature hydrogen ovens. The facility also has a dedicated machine shop including standard equipment as well as two high precision machining oriented center areas. In addition to high power and cooling handling capabilities of the research laboratory space, it also has a vacuum components dedicated clean storage area and an optical finishing laboratory.

As can be seen from Figs. 9 and 10, the facility was outfitted with testing of millimeter wave/THz vacuum electronics devices specifically in mind and contains a 3,500 ASF Millimeter Wave and High Power Microwave Lab in which vacuum electron devices (VEDs) are tested. This particular lab features 480 VAC 3 Phase, 1,200A service and overhead rails for electrical power supply. The HVAC system of the building keeps the lab ambient temperature within ± 2° C, even with large heat loads. The building HVAC system also maintains positive pressure in the lab, ensuring cleanliness and preventing contamination for outside sources. The lab features a dedicated chilled water supply system that can provide up to 141 kW of continuous cooling for water cooled testing equipment. Bay doors and an overhead crane are used for careful assembly and movement of sensitive equipment at the new facility.

On site, the facility features a high precision prototype machine shop available for quick and accurate parts fabrication or repairs, without the need to send parts away or to contract out for new parts. Welding facilities (laser and TIG) are also included in this shop. Of particular importance is the fact that the facility will feature three nano-CNC machines (see below) which have been essential in developing near-THz devices (see Figs. 11-17). This was made possible through an extremely productive collaboration over the past seven years with DMG-Mori (one of the world’s largest machine tools manufacturers) where we had sole access to a prototype NN1000 nano-CNC machine capable of manu­facturing tenths of microns sized parts with tolerances on the order of nanometers, comparable to micro-processing technology capabilities. This is a high productivity, high precision 5-axis CNC mill with sub-µm tolerance capabilities (<50 nm /100 mm position error) and the capability of providing surface roughness on the 10’s of nm scale. This capability will be greatly expanded in the Spafford facility as a result of the decision by DMG-Mori to donate three nano-CNC machines (estimated cost of each of the machines cost about $ 1.5 M as configured) to the DMRC which will be sited at the Spafford facility (see Fig. 6). Complete support capability ranging from preparation to final measurement is provided at the Spafford facility (see Fig. 7).

Figure 5: Spafford Rd. Laboratory

Figure 6: Spafford Road facility Layout; note the isolation pad specifically prepared for the Nano-CNC Machines used in near-THz device fabrication

Fig. 10. Photograph of a monocrystal diamond scribe (left), and a comparison of circuits fabricated with a conventional tungsten carbide tool (middle) versus a diamond tool (right).

Fig. 11. 220 GHZ SBTWT circuit fabricated at DTL, showing selected SEM images.

Professor Luhmann is collaborating with Prof. Islam in the vacuum nanoelectronics area.

Growth Capability: Islam group has a cold-wall CVD reactor (Figure 26, left) from First Nano (CVD Equipment Corporation, NY) and has capabilities of growing semiconductor (Si, Ge, diamond) thin films and nano materials. The reactor has gases for both p and n-type doping of thin films and nano-columns, nanowires and nanowalls of Si, Ge and GaP. The tool is also equipped with in-situ electrical probing capability. The tool will be used for the growth of some pn and pin epi-layers.

Figure 26. (left) A customized Chemical Vapor Deposition (CVD) process tool for semiconductor crystal growth is possessed by Islam group; (middle) Schematics of a custom-built transfer printing tool in Islam’s lab for transfer printing of devices from mother substrates to secondary substrates; (Right) Photograph of the device printing tool.

Islam’s Lab has equipment for the characterization of a wide range of semiconductor devices and optical systems. The equipment and facilities for the PDs and PV characterization broadly fall under three categories: (1) Optoelectronic device characterization (2) Electrical device characterization and (3) High-speed device characterizations.

For the electrical characterization, current-voltage (I-V) and capacitance-voltage (C-V) measurements, Islam has HP4155B semiconductor parameter analyzer and Agilent/HP 4284A Precision LCR Meter. We have PV measurement equipment including Solar Cell Quantum Efficiency Measurement System and Solar Cell I-V Measurement System. This system irradiates solar cells with measures the I-V curve and computes critical parameters such as V_oc, I_sc, J_sc, V_max, I_max, P_max, and efficiency. Our system includes the light source and the measurement equipment needed to measure I-V curves for solar cells. Its solar simulator illuminates the test device while the electronic load sweeps the cell voltage from a reverse-bias condition, through the power quadrant, and beyond Voc. The system’s computer gathers data, calculates solar cell parameters, generates printable test reports, and saves test data in text files.

Simulation Tools: Prof. Islam has the capability for simulating solar cells - device and processes using Silvaco TCAD. The simulation results can benefit the design and characterization of the solar cells. Silvaco Tcad can simulate the construction of solar cell doping and geometry, the open circuit voltage, short circuit current, the spectral response, the illuminated and un-illuminated I-V characteristics and quantum efficiency. Silvaco TCAD can incorporate FDTD into simple transfer matrix analysis for textured cell. The group also has COMSOL tool with wave optics module that offers capabilities for electromagnetic wave propagation in linear and nonlinear optical media for accurate component simulation and optical design optimization. To understand light-material interactions within complex nano-scale structures and materials, the group uses Lumerical Solution as photonic simulation software that has great capabilities to address the most of design problems across a wide range of applications. For the optical characterization, such as transmission and reflection measurements Islam group has an Ocean Optics spectrometer (200 nm-1100 nm).

Figure 27. DC and high speed test setup. (A) Digital sampling oscilloscope and high speed probe station (B) (Top) Fiber based femtosecond laser (FPL) (Left bottom) Fiber coupled laser source (right bottom) SuperK SELECT multi-line tunable filter (C) SuperK EXTREME supercontinuum lasers for 500-2200nm wavelngths. (D) (down respectively) Calibrated Reference Cell and Meter, Quartz WindowKeithley 2400 Digital Sourcemeter and Newport Oriel 69907 Universal Arc Lamp Power Supply (E) Newport 67005 Solar Simulator with 150W power.