Subash Khanal

Thermal Characterization of THz Schottky Diodes Using Transient Current Measurements

This paper presents a new method for thermal characterization of THz Schottky diodes. The method is based on the transient current behavior, and it enables the extraction of thermal resistances, thermal time-constants, and peak junction temperatures of THz Schottky diodes. Many typical challenges in thermal characterization of small-area diode devices, particularly those related to self-heating and electrical transients, are either avoided or mitigated. The method is validated with measurements of commercially available single-anode Schottky varactor diodes. A verification routine is performed to ensure the accuracy of the measurement setup, and the characterization results are compared against an in-house measurement-based method and against simulation results of two commercial 3-D thermal simulators. For example, characterization result for the total thermal resistance of a Schottky diode with an anode area of 9 μm2 is within 10% of the average value of 4020 K/W when using all four approaches. The new method can be used to measure small diode devices with thermal time constants down to about 300 ns with the measurement setup described in the paper.

Suitability of roll-to-roll reverse offset printing for mass production of millimeter-wave antennas: Progress report

In this work, we investigate different printing technologies suitable for mass production of millimeter-wave antennas and other devices, e.g., holograms and frequency selective absorbers, on flexible substrates. We concentrate especially on roll-to-roll reverse offset printing. The driving factors are low cost, high accuracy, high efficiency, and reliable performance. Therefore, we need to find and characterize suitable flexible substrates (permittivity and loss tangent at mm-wavelengths), conducting inks (viscosity, surface resistance of the resulting conducting layer), adhesion of the ink to the substrate, and feature size capable for printing mm-wave antennas and other passive devices in high volumes.

Towards printed millimeter-wave components: Material characterization

This paper presents the results from evaluation of suitable materials and ink properties for printing millimeter wave components. Dielectric parameters (relative permittivity and loss tangent) of various potential substrate materials are extracted from S-parameter measurements and simulations. Test samples have been printed over Polyethylene Terephthalate (PET) and Polyethylene Naphthalate (PEN) substrates and the measurement of the ink properties have been carried out.

Characterisation of low-barrier Schottky diodes for millimeter wave mixer applications

This paper presents the characterization measurements and simulations performed with ACST InGaAs low-barrier Schottky diodes for millimeter wave mixing applications. While these low-barrier Schottky diodes have been successfully used for millimeter wave detector design, their performance when acting as mixers has not been tested yet. This paper shows the performance for this type of diodes in a fundamental mixing configuration with evaluation of conversion loss and noise temperature. A fundamental mixer test-jig is used as the measurement platform with low-loss E-H impedance tuners for RF and LO signal matching. In addition to the measurements, 3D HFSS and ADS circuit simulations are also performed and results are presented. Conversion loss of less than 5 dB is obtained for 0.1 mW LO power in mixer operation at 181-183 GHz.

Experimental investigation of traps in THz Schottky diodes

In this paper, indications of charge trapping in THz Schottky diodes are investigated with various measurement techniques including current-voltage, capacitance and low-frequency noise measurements. GaAs diodes from various manufacturers are tested. For comparison purposes, results for two different diode samples are presented. Correlation between different measurement techniques is observed which indicate the presence of traps in measured Schottky diode samples. I-V and C-V measurements show some trapping behavior. However, it is also important to observe frequency dependency of the diode capacitance and low-frequency noise properties to closely monitor the charge trapping in small area Schottky diodes. Diode samples are measured in on-wafer environment using a probe station.