Abstract
This article presents a 135–150-GHz Schottky diode-based bias-less frequency tripler based on SU-8 micromachined WR-5 waveguides. The waveguides consist of five 432- $\mu \text{m}$ -thick silver-plated SU-8 layers, which house the diode chip and form the output matching network. The input matching circuit is realized in a computer numerical control (CNC) milled waveguide filter, which also provides support and thermal sink to the SU-8 waveguides. Considering the low thermal conductivity of the SU-8 material, auxiliary metallic thermal paths are designed, and the impact of these is discussed through thermal modeling. The thermal simulations show that under 50-mW power dissipation in the diode anodes, the maximum temperature of the SU-8 tripler is predicted to be 346 K at the diode junction, only 7 K higher than in an entirely metal equivalent. The tripler was measured to have a conversion loss of 16–18 dB and the input return loss is better than 18 dB. This work demonstrates that SU-8 micromachined waveguides can be used to package high-frequency semiconductor components, which, like other photolithography-based processes such as silicon deep reactive ion etching (Si-DRIE), has the potential for submicrometer feature resolution.
Highlights
I N THE past few decades, millimeter and terahertz (THz) waves have been found very useful in applications such as imaging [1]–[3], high-speed communication [4], [5], remoteManuscript received May 26, 2019; revised September 16, 2019; accepted November 8, 2019
Because the thermal conductivity of SU-8 is much lower than metal, we report on thermal designs and simulations performed to evaluate the steady-state temperature of this SU8-based device under nominal power dissipation
For the SU-8 tripler, the input filter was computer numerical control (CNC) machined from aluminum with the block split in the E-plane
Summary
I N THE past few decades, millimeter and terahertz (THz) waves have been found very useful in applications such as imaging [1]–[3], high-speed communication [4], [5], remote. Apart from CNC milling, several photolithography-based micromachining technologies have been reported to be capable of producing 3-D structures with high accuracy and large aspect ratio and of facilitating large-scale inexpensive fabrication These techniques include silicon deep reactive ion etching (Si-DRIE) [10], [11], LIthographie, Galvanoformung and Abformung (LIGA) [12], metal electroforming [13], [14], and SU-8 photoresist technology [15]–[20]. In our previous work, we have achieved an insertion loss as low as 0.048 and 0.031 dB/mm for WR-3 waveguides (220–325 GHz, waveguide dimensions: 0.864 mm × 0.432 mm) made from single- and double-deposition SU-8 layers, respectively [15] This is comparable to the performance of milled and gold-plated metallic waveguide (0.021 dB/mm) [15]. The successful demonstration of tripler made from multiple SU-8 layers represents a substantial and comprehensive step forward in the development of SU-8 micromachined devices
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