Adam M. Rowen

Design, fabrication, and characterization of metal micromachined rectangular waveguides at 3 THz

Single-mode 75 mum x 37 mum rectangular waveguide components, including horn antennas, couplers, and bends, for operation at 3 THz have been designed and fabricated using thick gold micromachining. THz transmission through these waveguides has been quasi-optically measured at 2.92 THz. This technology offers the potential for realizing miniature integrated systems operating in the 3 THz frequency range.

Properties of Surface Metal Micromachined Rectangular Waveguide Operating Near 3 THz

Single-mode TE10 rectangular waveguides operating near 3 THz have been demonstrated. The waveguides have internal dimensions of 75 μm × 37 μm (WR-0.3) and are fabricated using an additive gold electroplating process on a silicon substrate. The impact of photoresist removal holes was minimized by full-wave design of the hole and matching structures. Waveguides were measured at three frequencies from 2.56 to 3.11 THz and demonstrated loss as low as 1.3 dB/mm at 3.11 THz, corresponding to a loss per wavelength of 0.12 dB/λ. This paper summarizes the design, fabrication, and measurement of these micromachined waveguides operating near 3 THz.

Terahertz quantum cascade laser integration with on-chip micromachined rectangular waveguides

Integration of THz quantum cascade lasers (QCLs) with single-mode 75 μm x 37 μm rectangular waveguide components, including horn antennas, couplers, and bends, for operation at 3 THz has been designed and fabricated using thick gold micromachining. Measurements on the isolated waveguide components exhibit fairly low loss and integration with THz QCLs has been demonstrated. This technology offers the potential for realizing miniature integrated systems operating in the 3 THz frequency range.

Integrated chip-scale THz technology

The quantum cascade laser (QCL) is currently the only solid-state source of coherent THz radiation capable of delivering more than 1 mW of average power at frequencies above ~ 2 THz. This power level combined with very good intrinsic frequency definition characteristics make QCLs an extremely appealing solid-state solution as compact sources for THz applications. I will present results on integrating QCLs with passive rectangular waveguides for guiding and controlling the radiation emitted by the QCLs and on the performance of a THz integrated circuit combining a THz QCL with a Schottky diode mixer to form a heterodyne receiver/transceiver.

Micro-fabricated stylus ion trap

An electroformed, three-dimensional stylus Paul trap was designed to confine a single atomic ion for use as a sensor to probe the electric-field noise of proximate surfaces. The trap was microfabricated with the UV-LIGA technique to reduce the distance of the ion from the surface of interest. We detail the fabrication process used to produce a 150 μm tall stylus trap with feature sizes of 40 μm. We confined single, laser-cooled, (25)Mg(+) ions with lifetimes greater than 2 h above the stylus trap in an ultra-high-vacuum environment. After cooling a motional mode of the ion at 4 MHz close to its ground state ( = 0.34 ± 0.07), the heating rate of the trap was measured with Raman sideband spectroscopy to be 387 ± 15 quanta/s at an ion height of 62 μm above the stylus electrodes.

Multilayer metal micromachining for THz waveguide fabrication

Thick multi-layer metal stacking offers the potential for fabrication of rectangular waveguide components, including horn antennas, couplers, and bends, for operation at terahertz frequencies, which are too small to machine traditionally. Air-filled, TE10, rectangular waveguides for 3 THz operation were fabricated using two stacked electroplated gold layers on both planar and non-planar substrates. The initial layer of lithography and electroplating defined 37 micrometer tall waveguide walls in both straight and meandering geometries. The second layer, processed on top of the first, defined 33 micrometer thick waveguide lids. Release holes periodically spaced along the center of the lids improved resist clearing from inside of the electroformed rectangular channels. Processing tests of hollow structures on optically clear, lithium disilicate substrates allowed confirmation of resist removal by backside inspection.

Optimizing galvanic pulse plating parameters to improve indium bump to bump bonding

The plating characteristics of a commercially available indium plating solution are examined and optimized to help meet the increasing performance demands of integrated circuits requiring substantial numbers of electrical interconnections over large areas. Current fabrication techniques rely on evaporation of soft metals, such as indium, into lift-off resist profiles. This becomes increasingly difficult to accomplish as pitches decrease and aspect ratios increase. To minimize pixel dimensions and maximize the number of pixels per unit area, lithography and electrochemical deposition (ECD) of indium has been investigated. Pulse ECD offers the capability of improving large area uniformity ideal for large area device hybridization. Electrochemical experimentation into lithographically patterned molds allow for large areas of bumps to be fabricated for low temperature indium to indium bonds. The galvanic pulse profile, in conjunction with the bath configuration, determines the uniformity of the plated array. This pulse is manipulated to produce optimal properties for hybridizing arrays of aligned and bonded indium bumps. The physical properties of the indium bump arrays are examined using a white light interferometer, a SEM and tensile pull testing. This paper provides details from the electroplating processes as well as conclusions leading to optimized plating conditions.

Fabrication of lattice mismatched multijunction photovoltaic cells using 3D integration concepts

We present the experimental procedure to create lattice mismatched multijunction photovoltaic (PV) cells using 3D integration concepts. Lattice mismatched multijunction photovoltaic (PV) cells with decoupled electrical outputs could achieve higher efficiencies than current-matched monolithic devices. Growing lattice mismatched materials as a monolithic structure generates defects and decreases performance. We propose using methods from the integrated circuits and microsystems arena to produce the PV cell. The fabricated device consists of an ultrathin (6 μm) series connected InGaP/GaAs PV cell mechanically stacked on top of an electrically independent silicon cell. The InGaP/GaAs PV cell was processed to produce a small cell (750 μm) with back-contacts where all of the contacts sit at the same level. The dual junction and the silicon (c-Si) cell are electrically decoupled and the power from both cells is accessible through pads on the c-Si PV cell. Through this approach, we were able to fabricate a functional double junction PV cell mechanically attached to a c-Si PV cell with independent connections.

Integration of terahertz quantum cascade lasers with lithographically micromachined waveguides

Gold rectangular waveguides suitable for single mode operation at frequencies near 3 THz have been micromachined using silicon microfabrication methods. The design, fabrication, and loss characteristics of these waveguides will be presented. On-chip integration of these waveguide structures with THz quantum cascade laser (QCL) sources has been achieved and the characteristics of QCL beams guided by waveguide will be discussed.

Microfabricated Wire Arrays for Z-Pinch

Microfabrication methods have been applied to the fabrication of wire arrays suitable for use in Z. Self-curling GaAs/AlGaAs supports were fabricated as an initial route to make small wire arrays (4mm diameter). A strain relief structure that could be integrated with the wire was designed to allow displacements of the anode/cathode connections in Z. Electroplated gold wire arrays with integrated anode/cathode bus connections were found to be sufficiently robust to allow direct handling. Platinum and copper plating processes were also investigated. A process to fabricate wire arrays on any substrate with wire thickness up to 35 microns was developed. Methods to handle and mount these arrays were developed. Fabrication of wire arrays of 20mm diameter was demonstrated, and the path to 40mm array fabrication is clear. With some final investment to show array mounting into Z hardware, the entire process to produce a microfabricated wire array will have been demonstrated.