Aik Yean Tang

Impact of Eddy Currents and Crowding Effects on High-Frequency Losses in Planar Schottky Diodes

In this paper, we present the influence of eddy currents, skin and proximity effects on high-frequency losses in planar terahertz Schottky diodes. The high-frequency losses, particularly losses due to the spreading resistance, are analyzed as a function of the ohmic-contact mesa geometry for frequencies up to 600 GHz. A combination of 3-D electromagnetic (EM) simulations and parameter extraction based on lumped equivalent circuit is used for the analysis. The extracted low-frequency spreading resistance shows a good agreement with the results from electrostatic simulations and experimental data. By taking into consideration the EM field couplings, the analysis shows that the optimum ohmic-contact mesa thickness is approximately one-skin depth at the operating frequency. It is also shown that, for a typical diode, the onset of eddy current loss starts at ~ 200 GHz, and the onset of a mixture of skin and proximity effects occurs around ~ 400 GHz.

Electro-Thermal Model for Multi-Anode Schottky Diode Multipliers

We present a self-consistent electro-thermal model for multi-anode Schottky diode multiplier circuits. The thermal model is developed for an n-anode multiplier via a thermal resistance matrix approach. The nonlinear temperature responses of the material are taken into consideration by using a linear temperature-dependent approximation for the thermal resistance. The electro-thermal model is capable of predicting the hot spot temperature, providing useful information for circuit reliability study as well as high power circuit design and optimization. Examples of the circuit analysis incorporating the electro-thermal model for a substrateless- and a membrane-based multiplier circuits, operating up to 200 GHz, are demonstrated. Compared to simulations without thermal model, the simulations with electro-thermal model agree better with the measurement results. For the substrateless multiplier, the error between the simulated and measured peak output power is reduced from ~ 13% to ~ 4% by including the thermal effect.

Development of a 557 GHz GaAs monolithic membrane-diode mixer

We present the development of a monolithically integrated 557 GHz membrane Schottky diode mixer. RF test shows state-of-the-art performance with an optimum receiver noise temperature below 1300 K DSB and an estimated mixer DSB conversion loss of 9 dB and a mixer DSB noise temperature of 1100 K including all losses.

Submillimeter Wave

We demonstrate S-parameter characterization of membrane circuits in the WR-03 frequency band (220-325 GHz) utilizing thru-reflect-line (TRL) -calibration technique. The TRL calibration kit design features 3 μm thick GaAs membrane circuits packaged in E-plane split waveguide blocks with the reference planes inside the membrane circuit structure. A 300 GHz membrane ring resonator filter circuit has been characterized by applying the proposed calibration kit, showing good agreement with simulations.

{\rm S}

3-D models have been developed to study the series resistance (Rs) at DC and the extrinsic parasitic elements (capacitance and inductance) at high frequencies for a Schottky diode chip. For the Rs study, a comparison with the experimental result has been carried out. High frequency properties and the corresponding S-parameters of the Schottky diode chip are simulated using a 3-D finite element electromagnetic solver. The parasitic elements are then extracted and studied as a function of the diode geometry. The outcome of the studies shows the existence of a significant pad-to-pad capacitance through the semi-insulating substrate which could be improved by implementing tapered shape pads.

-Parameter Characterization of Integrated Membrane Circuits

We present a sensitivity analysis on TRL calibrated S-parameter measurements of membrane circuits in the WR-03 waveguide band (220-325 GHz). The impact of waveguide and membrane circuit misalignment, as well as waveguide dimension mismatch is investigated. The analysis is performed for the thru-reflect-line (TRL) calibration applied to E-plane split waveguide blocks carrying membrane circuits. The analysis shows a large influence of the waveguide width tolerance on transmission and reflection phase after the TRL calibration. For a 20 mm long rectangular waveguide with a ± 5 μm width tolerance a phase uncertainty as large as ± 45° for reflection and ± 30° for transmission measurements is observed.

Modeling of GaAs Schottky diodes for terahertz application

We report on a heterodyne terahertz spectrometer based on a fully integrated 557-GHz receiver and a digital fast Fourier transform spectrometer. The receiver consists of a chain of multipliers and power amplifiers, followed by a heterostructure barrier varactor tripler that subharmonically pumps a membrane GaAs Schottky diode mixer. All sub-components are newly developed and optimized with regard to the overall receiver performance such as noise temperature, power consumption, weight and physical size. The receiver works at room temperature, has a double sideband noise temperature as low as 2000 K at a maximum power consumption of 4.5 W with an Allan time of 10 s and a sideband gain ratio of 0.52. The performance of the spectrometer is demonstrated by absorption spectroscopy of H2O and CH3OH with an instantaneous bandwidth of 1.5 GHz and a resolution of 183 kHz. Several pressure broadening parameters of methanol absorption lines were determined, that agree with other published data. Using the experimentally determined molecular parameters the CH3OH absorption spectrum could be modeled with very high precision.

Sensitivity Analysis of TRL Calibration in Waveguide Integrated Membrane Circuits

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.

Molecular Spectroscopy With a Compact 557-GHz Heterodyne Receiver

A TRL-calibration kit enabling S-parameter characterization of membrane circuits has been developed for the WR-03 band. The TRL-design features 3 µm thick GaAs membrane circuits packaged in E-plane split waveguide blocks. Membrane filters have been characterized after the calibration.

Thermal Characterization of THz Schottky Diodes Using Transient Current Measurements

Spreading resistance of a planar Schottky diode is studied as a function of the frequency and buffer layer thickness. The study shows an increase of effective high frequency resistance for a buffer layer thicker than skin depth, due to the parasitic capacitances induced current in buffer layer.