200, 400 and 800 GHz Schottky diode substrateless multipliers: design and results
Several sub-millimeter doubler circuits have been designed and built using a new fabrication technology.
Schottky diodes multipliers monolithic circuits↗
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A 1.2 THz planar tripler using GaAs membrane based clips
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Schottky diodes multipliers monolithic circuits↗
Monolithic frequency doublers and triplers for THz frequencies
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Schottky diodes multipliers monolithic circuits↗
THz multiplier circuits
Planar Schottky diode technology has been utilized to fabricate high-power broad-band monolithic multiplier circuits that can produce appreciable power well into the THz range. The chip fabrication technology that has been developed allows for robust circuit designs that can be easily packaged in conventional waveguide blocks. An overview of the capability of GaAs based Schottky diode multipliers will be presented.
Maestrini, A.↗
Performance of a 1.2 THz frequency tripler using a GaAs frameless membrane monolithic circuit
A tunerless 1.2 THz waveguide frequency tripler using Schottky planar varactor diodes has been designed, fabricated and tested.
Schotkky diodes multipliers monolithic circuits↗
670-GHz Schottky Diode-Based Subharmonic Mixer with CPW Circuits and 70-GHz IF
GaAs-based, sub-harmonically pumped Schottky diode mixers offer a number of advantages for array implementation in a heterodyne receiver system. Since the radio frequency (RF) and local oscillator (LO) signals are far apart, system design becomes much simpler. A proprietary planar GaAs Schottky diode process was developed that results in very low parasitic anodes that have cutoff frequencies in the tens of terahertz. This technology enables robust implementation of monolithic mixer and frequency multiplier circuits well into the terahertz frequency range. Using optical and e-beam lithography, and conventional epitaxial layer design with innovative usage of GaAs membranes and metal beam leads, high-performance terahertz circuits can be designed with high fidelity. All of these mixers use metal waveguide structures for housing. Metal machined structures for RF and LO coupling hamper these mixers to be integrated in multi-pixel heterodyne array receivers for spectroscopic and imaging applications. Moreover, the recent developments of terahertz transistors on InP substrate provide an opportunity, for the first time, to have integrated amplifiers followed by Schottky diode mixers in a heterodyne receiver at these frequencies. Since the amplifiers are developed on a planar architecture to facilitate multi-pixel array implementation, it is quite important to find alternative architecture to waveguide-based mixers.
Chattopadhyay, Goutam↗
100-GHz Phase Switch/Mixer Containing a Slot-Line Transition
A circuit that can function as a phase switch, frequency mixer, or frequency multiplier operates over a broad frequency range in the vicinity of 100 GHz. Among the most notable features of this circuit is a grounded uniplanar transition (in effect, a balun) between a slot line and one of two coplanar waveguides (CPWs). The design of this circuit is well suited to integration of the circuit into a microwave monolithic integrated circuit (MMIC) package. One CPW is located at the input end and one at the output end of the top side of a substrate on which the circuit is fabricated (see Figure 1). The input CPW feeds the input signal to antiparallel flip-chip Schottky diodes connected to the edges of the slot line. Phase switching is effected by the combination of (1) the abrupt transition from the input CPW to the slot line and (2) CPW ground tuning effected by switching of the bias on the diodes. Grounding of the slot metal to the bottom metal gives rise to a frequency cutoff in the slot. This cutoff is valuable for separating different frequency components when the circuit is used as a mixer or multiplier. Proceeding along the slot line toward the output end, one encounters the aforementioned transition, which couples the slot line to the output CPW. Impedance tuning of the transition is accomplished by use of a high-impedance section immediately before the transition.
Gaier, Todd↗
System-on-chip upgrade of millimeter-wave imaging diagnostics for fusion plasma
Monolithic, millimeter wave “system-on-chip” technology has been employed in chip heterodyne radiometers in a newly developed Electron Cyclotron Emission Imaging (ECEI) system on the DIII-D tokamak for 2D electron temperature and fluctuation diagnostics. The system employs 20 horn-waveguide receiver modules each with customized W-band (75–110 GHz) monolithic microwave integrated circuit chips comprising a W-band low noise amplifier, a balanced mixer, a ×2 local oscillator (LO) frequency doubler, and two intermediate frequency amplifier stages in each module. Compared to previous quasi-optical ECEI arrays with Schottky mixer diodes mounted on planar antennas, the upgraded W-band array exhibits >30 dB additional gain and 20× improvement in noise temperature; an internal eight times multiplier chain is used to provide LO coupling, thereby eliminating the need for quasi-optical coupling. The horn-waveguide shielding housing avoids out-of-band noise interference on each module. The upgraded ECEI system plays an important role for absolute electron temperature and fluctuation measurements for edge and core region transport physics studies. An F-band receiver chip (up to 140 GHz) is under development for additional fusion facilities with a higher toroidal magnetic field. Visualization diagnostics provide multi-scale and multi-dimensional data in plasma profile evolution. Finally, a significant aspect of imaging measurement is focusing on artificial intelligence for science applications.
47 OTHER INSTRUMENTATION↗
Power Amplifier Module with 734-mW Continuous Wave Output Power
Research findings were reported from an investigation of new gallium nitride (GaN) monolithic millimeter-wave integrated circuit (MMIC) power amplifiers (PAs) targeting the highest output power and the highest efficiency for class-A operation in W-band (75-110 GHz). W-band PAs are a major component of many frequency multiplied submillimeter-wave LO signal sources. For spectrometer arrays, substantial W-band power is required due to the passive lossy frequency multipliers-to generate higher frequency signals in nonlinear Schottky diode-based LO sources. By advancing PA technology, the LO system performance can be increased with possible cost reductions compared to current GaAs PAs. High-power, high-efficiency GaN PAs are cross-cutting and can enable more efficient local oscillator distribution systems for new astrophysics and planetary receivers and heterodyne array instruments. It can also allow for a new, electronically scannable solid-state array technology for future Earth science radar instruments and communications platforms.
Fung, King Man↗
A 1.2 THz Planar Tripler Using GaAs Membrane Based Chips
Fabrication technology for submillimeter-wave monolithic circuits has made tremendous progress in recent years and it is now possible to fabricate sub-micron GaAs Schottky devices on a number of substrate types, such as membranes, frame-less membranes or substrateless circuits. These new technologies allow designers to implement very high frequency circuits, either Schottky mixers or multipliers, in a radically new manner. This paper will address the design, fabrication, and preliminary results of a 1.2 THz planar tripler fabricated on a GaAs frame-less membrane, the concept of which was described previously. The tripler uses a diode pair in an antiparallel configuration similar to designs used at lower frequency. To date, this tripler has produced a peak output power of 80 microW with 0.9% efficiency at room temperature (at 1126 GHz). The measured fix-tuned 3 dB bandwidth is about 3.5%. When cooled, the output power reached a peak of 195 microW at 120 K and 250 microW at 50 K. The ease with which this circuit was implemented along with the superb achieved performance indicates that properly designed planar devices such as this tripler can now usher in a new era of practical very high frequency multipliers.
Bruston, J.↗
Millimeter-wave diode-grid frequency doubler
Monolithic diode grids were fabricated on 2-cm square gallium-arsenide wafers in a proof-of-principle test of a quasi-optical varactor millimeter-wave frequency multiplier array concept. An equivalent circuit model based on a transmission-line analysis of plane wave illumination was applied to predict the array performance. The doubler experiments were performed under far-field illumination conditions. A second-harmonic conversion efficiency of 9.5 percent and output powers of 0.5 W were achieved at 66 GHz when the diode grid was pumped with a pulsed source at 33 GHz. This grid had 760 Schottky-barrier varactor diodes. The average series resistance was 27 ohms, the minimum capacitance was 18 fF at a reverse breakdown voltage of -3 V. The measurements indicate that the diode grid is a feasible device for generating watt-level powers at millimeter frequencies and that substantial improvement is possible by improving the diode breakdown voltage.
Jou, Christina F.↗
Biasable Subharmonic Membrane Mixer for 520 to 600 GHz
The figure shows a biasable subharmonic mixer designed to operate in the frequency range from 520 to 600 GHz. This mixer is a prototype of low-power mixers needed for development of wideband, high-resolution spectrometers for measuring spectra of molecules in the atmospheres of Earth, other planets, and comets in the frequency range of 400 to 700 GHz. Three considerations dictated the main features of the design: It is highly desirable to operate the spectrometers at or slightly below room temperature. This consideration is addressed by choosing Schottky diodes as the frequency-mixing circuit elements because of all mixer diodes, Schottky diodes are the best candidates for affording sufficient sensitivity at or slightly below room-temperature range. The short wavelengths in the intended operating-frequency range translate to stringent requirements for precision of fabrication and assembly of the circuits; these requirements are even more stringent for wide-bandwidth circuits. This consideration is addressed in two ways: (1) As much as possible of the mixer circuitry is fabricated in the form of a monolithic integrated circuit on a GaAs membrane, employing a modified version of a process used previously to fabricate a non-subharmonic mixer for a frequency of 2.5 THz and frequency multipliers for frequencies up to 2 THz. (2) The remainder of the circuitry is precision machined into a waveguide block that holds the GaAs integrated circuit.
Schlecht, Erich↗
W-band system-on-chip electron cyclotron emission imaging system on DIII-D
Monolithic, millimeter wave “system-on-chip” (SoC) technology has been employed in heterodyne receiver integrated circuit radiometers in a newly developed Electron Cyclotron Emission Imaging (ECEI) system on the DIII-D tokamak for 2D electron temperature profile and fluctuation evolution diagnostics. Here, a prototype module operating in E-band (72-80 GHz) was first employed in a 2 x 10 element array that demonstrated significant improvements over the previous quasi-optical Schottky diode mixer arrays during the 2018 operational campaign of the DIII-D tokamak. For compatibility with International Thermonuclear Experimental Reactor (ITER) relevant scenarios on DIII-D, the SoC ECEI system was upgraded with 20 horn-waveguide receiver modules. Each individual module contains a University of California at Davis designed W-band (75 -110 GHz) receiver die that integrates a broadband low noise amplifier (LNA), a double balanced down-converting mixer, and a x4 multiplier on the local oscillator (LO) chain. A x2 multiplier and two IF amplifiers are packaged and selected to further boost the signal strength as well as downconvert the signal frequency. The upgraded W-band array exhibits > 30 dB additional gain and 20x improvement in noise temperature comparing with the previous Schottky diode radio frequency (RF) mixer input systems; an internal 8 times multiplier chain is used to bring down the LO frequency below 12 GHz, thereby obviating the need for a large aperture for quasi-optical LO coupling and replacing it with coaxial connectors. The horn-waveguide shielding housing avoids out-of-band noise interference on each individual module. The upgraded ECEI system plays an important role for absolute electron temperature evolution and fluctuation measurements for edge and core region transport physics studies.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
An All-Solid-State, Room-Temperature, Heterodyne Receiver for Atmospheric Spectroscopy at 1.2 THz
Heterodyne receivers at submillimeter wavelengths have played a major role in astrophysics as well as Earth and planetary remote sensing. All-solid-state heterodyne receivers using both MMIC (monolithic microwave integrated circuit) Schottky-diode-based LO (local oscillator) sources and mixers are uniquely suited for long-term planetary missions or Earth climate monitoring missions as they can operate for decades without the need for any active cryogenic cooling. However, the main concern in using Schottky-diode-based mixers at frequencies beyond 1 THz has been the lack of enough LO power to drive the devices because 1 to 3 mW are required to properly pump Schottky diode mixers. Recent progress in HEMT- (high-electron-mobility- transistor) based power amplifier technology, with output power levels in excess of 1 W recently demonstrated at W-band, as well as advances in MMIC Schottky diode circuit technology, have led to measured output powers up to 1.4 mW at 0.9 THz. Here the first room-temperature tunable, all-planar, Schottky-diode-based receiver is reported that is operating at 1.2 THz over a wide (≈20%) bandwidth. The receiver front-end (see figure) consists of a Schottky-diode-based 540 to 640 GHz multiplied LO chain (featuring a cascade of W-band power amplifiers providing around 120 to 180 mW at W-band), a 200-GHz MMIC frequency doubler, and a 600-GHz MMIC frequency tripler, plus a biasable 1.2-THz MMIC sub-harmonic Schottky-diode mixer. The LO chain has been designed, fabricated, and tested at JPL and provides around 1 to 1.5 mW at 540 o 640 GHz. The sub-harmonic mixer consists of two Schottky diodes on a thin GaAs membrane in an anti-parallel configuration. An integrated metal insulator metal (MIM) capacitor has been included on-chip to allow dc bias for the Schottky diodes. A bias voltage of around 0.5 V/diode is necessary to reduce the LO power required down to the 1 to 1.5 mW available from the LO chain. The epilayer thickness and doping profiles have been specifically optimized to maximize the mixer performance beyond 1 THz. The measured DSB noise temperatures and conversion losses of the receiver are 2,000 to 3,500 K and 12 to 14 dB, respectively, at 120 K, and 4,000 to 6,000 K and 13 to 15 dB, respectively, at 300 K. These results establish the state-of-the-art for all-solid-state, all-planar heterodyne receivers at 1.2 THz operating at either room temperature or using passive cooling only. Since no cryogenic cooling is needed, the receiver is eminently suited to atmospheric heterodyne spectroscopy of the outer planets and their moons.
Siles, Jose V.↗