Jose V. Siles

Design and Characterization of a Room Temperature All-Solid-State Electronic Source Tunable From 2.48 to 2.75 THz

We report on the design, fabrication and test of an all-solid-state, frequency agile source that produces over across the 2.48-2.75 THz band at room temperature. This frequency-multiplied source is driven by a W-band synthesizer followed by a power amplifier that delivers 350-450 mW (25.5-26.5 dBm) and a cascade of three balanced frequency triplers. The first stage tripler is based on four power-combined six-anode GaAs Schottky diode devices, and the second stage tripler is based on two four-anode GaAs devices. The output tripler uses a single unbiased device featuring two anodes monolithically integrated onto a thin GaAs membrane. The source delivers a record at 2.58 THz at room temperature. This frequency multiplied source is analyzed with a Fourier transform spectrometer (FTS) and the unwanted harmonics are found to be at least 29 dB below the desired signal. This source, when used as the local oscillator for a hot-electron bolometer mixer, will enable heterodyne instruments for future space missions to map the cosmologically-important 2.675 THz HD molecular line.

A High-Power 105–120 GHz Broadband On-Chip Power-Combined Frequency Tripler

We report on the design, fabrication and characterization of a high-power and broadband 105-120 GHz Schottky diode frequency tripler based on a novel on-chip power combining concept that allows superior power handling than traditional approaches. The chip features twelve anodes on a 50 μm thick GaAs substrate. At room temperature, the tripler exhibits a 17% 3 dB bandwidth and a ~ 30% peak conversion efficiency for a nominal input power of around 350-400 mW, and ~ 20% efficiency for its maximum operational input power of 800-900 mW. This tripler can deliver maximum power levels very close to 200 mW. The on-chip power-combined frequency tripler is compared with a traditional tripler designed for the same band using the same design parameters.

A Silicon Micromachined Eight-Pixel Transceiver Array for Submillimeter-Wave Radar

An eight-pixel transceiver array for operation in a 340 GHz imaging radar is presented. Silicon micromachining is applied to fabricate the submillimeter-wave front-end components to increase the density and uniformity of the array while lowering the cost compared to metal machining. Performance comparable with discrete metal machined housings was achieved with the 340 GHz transmitter nominally producing 0.5 mW and the mixers having a DSB noise temperature of 2000 K with a conversion loss of 8 dB. Radar performance is primarily limited by the isolation of the hybrid coupler, which is typically 28 dB, but excellent imaging performance is still achieved and improvements in penetration compared to higher frequency imaging radars is demonstrated.

Schottky Diode Based 1.2 THz Receivers Operating at Room-Temperature and Below for Planetary Atmospheric Sounding

In this paper, we report on the design, fabrication and test of two designs for all-solid-state planar Schottky diode based receivers working in the 1.2 THz range. At room temperature, a double side-band (DSB) mixer noise temperature of 2800 K and a conversion loss of 10.5 dB have been measured at 1134 GHz. When the mixers are cooled down to 120 K, they exhibit DSB noise temperatures as low as about 2000 K and conversion loss of 12 dB. The compact local oscillator source (LO) is based on a x2x3 chain and sufficiently pumps the sub-harmonic mixer with 1.5-2.5 mW of power. The receivers provide around 15% RF bandwidth and are well suited for planetary missions to investigate methane and other key lines.

Silicon microfabrication technologies for THz applications

Silicon micromachining technology is naturally suited for making THz components, where precision and accuracy are essentials. We report here the development of robust micromachining techniques to enable novel active and passive components in the submillimeter-wave region. These features will enable large format submillimeter-wave heterodyne arrays and 3-D integration in the THz region, where fabricating circuits and structures becomes difficult with conventional machining.

Array technology for terahertz imaging

Heterodyne terahertz (0.3 - 3THz) imaging systems are currently limited to single or a low number of pixels. Drastic improvements in imaging sensitivity and speed can be achieved by replacing single pixel systems with an array of detectors. This paper presents an array topology that is being developed at the Jet Propulsion Laboratory based on the micromachining of silicon. This technique fabricates the arrays package and waveguide components by plasma etching of silicon, resulting in devices with precision surpassing that of current metal machining techniques. Using silicon increases the versatility of the packaging, enabling a variety of orientations of circuitry within the device which increases circuit density and design options. The design of a two-pixel transceiver utilizing a stacked architecture is presented that achieves a pixel spacing of 10mm. By only allowing coupling from the top and bottom of the package the design can readily be arrayed in two dimensions with a spacing of 10mm x 18mm.

Transceiver array development for submillimeter-wave imaging radars

The Jet Propulsion Laboratory (JPL) is developing compact transceiver arrays housing discrete GaAs Schottky diodes with integrated waveguides in order to increase the frame rate and lower the cost of active submillimeter-wave imaging radar systems. As part of this effort, high performance diode frequency multiplier and mixer devices optimized for a 30 GHz bandwidth centered near 340 GHz have been fabricated using JPL’s MoMeD process. A two-element array unit cell was designed using a layered architecture with three-dimensional waveguide routing for maximum scalability to multiple array elements. Prototype two-element arrays have been built using both conventionally machined metal blocks as well as gold-plated micromachined silicon substrates. Preliminary performance characterization has been accomplished in terms of transmit power, and conversion loss, and promising 3D radar images of concealed weapons have been acquired using the array.

A Multistep DRIE Process for Complex Terahertz Waveguide Components

A silicon deep reactive-ion etching (DRIE) process has been developed, using multiple SiO2 masks to enable multidepth waveguide features with ±2% tolerance. The unique capability of this process is demonstrated by designing, fabricating, and testing an orthomode transducer working in the 500-600 GHz frequency range. Straight waveguide measurements are also performed to characterize the losses associated with the multistep DRIE process, giving results slightly better than expected for metal-machined waveguides. This process enables the integration of multiple terahertz waveguide components such as mixers, multipliers, quadrature hybrids, and polarization twists onto a single silicon package.

THz Diode Technology: Status, Prospects, and Applications

Found in many terahertz (THz) and submillimeter-wave systems, GaAs Schottky diodes continue to be one of the most useful THz devices. As a low-parasitic device that operates well into the THz range, Schottky diodes provide useful detection and power generation for a number of practical applications. Mixers and multipliers, working as high as ~3 THz, have already been demonstrated. This paper reviews the current status of diode technology, detailing some of the different ways for fabricating THz chips. An overview regarding the current state of technology and performance for THz frequency multipliers and mixers is presented, along with applications enabled by these diodes.

Terahertz array receivers with integrated antennas

Highly sensitive terahertz heterodyne receivers have been mostly single-pixel. However, now there is a real need of multi-pixel array receivers at these frequencies driven by the science and instrument requirements. In this paper we explore various receiver front-end and antenna architectures for use in multi-pixel integrated arrays at terahertz frequencies. Development of wafer-level integrated terahertz receiver front-end by using advanced semiconductor fabrication technologies has progressed very well over the past few years. Novel stacking of micro-machined silicon wafers which allows for the 3-dimensional integration of various terahertz receiver components in extremely small packages has made it possible to design multi-pixel heterodyne arrays. One of the critical technologies to achieve fully integrated system is the antenna arrays compatible with the receiver array architecture. In this paper we explore different receiver and antenna architectures for multi-pixel heterodyne and direct detector arrays for various applications such as multi-pixel high resolution spectrometer and imaging radar at terahertz frequencies.