Terahertz (THz) frequency radiometers, spectrometers, and radars are promising instruments for the remote sensing of planetary atmospheres such as Mars, Venus, Jupiter, and Saturn, and their moons such as Titan, Europa, Ganymede, and others. For these long-term planetary missions, severe constraints are put on the mass and power budget for the payload instruments.
One approach for fabricating highly integrated and compact submillimeter-wave transmitter/receiver front-ends is to integrate the W-band and higher-frequency power amplifiers, multipliers, and mixer chips into a single micromachined silicon block. This architecture shrinks the heterodyne receiver front-end elements by an order of magnitude in mass and size compared to conventional metal milling techniques.
Several different micromachining techniques exist for fabrication of these THz circuits, and silicon Deep Reactive Ion Etching (DRIE) was chosen because it offers a wider range of design possibilities while achieving better resolution. Silicon dioxide (SiO2) is used as the only mask or as additional mask for deep etches, to protect the silicon when the resist (PR) is etched away. On average, while doing DRIE, the selectivity PR:silicon ratio is 50:1, but for SiO2, a 150:1 selectivity can be achieved, making it a good hard mask candidate. SiO2 is either deposited with plasma-enhanced chemical vapor deposition (PECVD) or is thermally grown before processing the wafer.
The SiO2 mask is made with varying thicknesses over the wafer, chosen according to the depth of the silicon etch being masked. In this way, the series of etch patterns is exposed sequentially by removing increments of the SiO2 mask uniformly over the entire wafer. Crucially, all lithographic steps that define the multiple silicon etch depths are carried out in the SiO2 mask itself prior to the actual etching of silicon. Because the SiO2 only needs to be a few hundred nanometers deep, photoresist never has to be applied to a surface with few-hundred-micron scale trenches in it, thus avoiding the con-comitant coverage problems.
By using a predefined SiO2 hard mask and a cumulative DRIE etching process, parts can be fabricated that exhibit sharp edges and smooth etch bottoms with depths controlled to 2% tolerance, to form complex multi-depth structures. This process has already been used to fabricate numerous THz structures, and recent results validate the use of silicon for THz circuits as a batch-process alternative to conventional metal machining. This technique enables large pixel-count ultra-compact receiver architectures and extends the use of waveguide based components beyond 2 THz.
This work was done by Cecile Jung-Kubiak, Theodore J. Reck, Goutam Chattopadhyay, Jose V. Siles, Robert H. Lin, Imran Mehdi, Choonsup Lee, Ken B. Cooper, and Alejandro Peralta of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management JPL
Mail Stop 321-123
4800 Oak Grove Drive
Pasadena, CA 91109-8099
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Refer to NPO-49123.
This Brief includes a Technical Support Package (TSP).
Multi-Step DRIE Process to Fabricate Silicon-Based THz Components
(reference NPO49123) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) that focuses on the Multi-Step Deep Reactive Ion Etching (DRIE) process used to fabricate silicon-based terahertz (THz) components. It is part of NASA Tech Briefs, specifically referenced as NPO-49123, and aims to disseminate aerospace-related technological advancements that have broader scientific, commercial, and technological applications.
The document outlines the significance of terahertz technology, which operates in the frequency range between microwave and infrared, and its potential applications in various fields, including telecommunications, imaging, and sensing. The advancements in THz components are crucial for developing high-performance interconnects and receivers, which are essential for multi-pixel arrays used in various scientific and commercial applications.
Key components discussed in the document include:
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THz Canonical Filter: A device designed to filter specific terahertz frequencies, enhancing signal clarity and performance in THz systems.
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Stacked Silicon Micromachined Interconnect: This component facilitates efficient connections between THz devices, improving overall system integration and performance.
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Single-Pixel Silicon Micromachined Receiver: A receiver designed for capturing terahertz signals, which is vital for applications in imaging and sensing.
The document emphasizes the importance of the Multi-Step DRIE process, which allows for precise fabrication of these components, enabling the development of advanced THz systems. The process is noted for its ability to create intricate microstructures that are essential for the performance of THz devices.
Additionally, the document provides contact information for further inquiries related to research and technology in this area, specifically through the Innovative Technology Assets Management at JPL. It also includes a disclaimer regarding the use of the information contained within, stating that the U.S. Government does not assume liability for its application.
Overall, this Technical Support Package serves as a comprehensive resource for understanding the advancements in THz technology and the fabrication processes that support the development of innovative components, highlighting NASA's commitment to technology transfer and the broader implications of its research.
