Candidate: Amr Samir
Title: Silicon-Based Integration Technology for Terahertz Source
Date: April 5, 2023
Time: 4:00 PM
Place: E5 4047
Supervisor(s): Majedi, Hamed - Basha, Mohamed A. (Adjunct)
Abstract:
The Terahertz (THz) frequency spectrum offers solutions and opportunities to the new emerging technology applications which require high-quality THz sources, detectors, and integrated circuits. However, due to the high conduction loss at THz, it is not recommended to use on-chip integration of metallic planar transmission lines and passive components that vastly degrade the performance. Therefore, one of the promising methods to conveniently solve this problem is the integration of the active chips with high-quality off-chip passive components using a hybrid integrated packaging technology that is compatible, low loss, and precisely fabricated i.e. ultra-low length wire bonding.
The focus of this research is to investigate, design and develop a proof-of-concept prototype for the THz source integration on an efficient and inexpensive silicon-based integrated platform for terahertz applications. A design of 0.5 THz source based on two-cascaded frequency Tripler stages using anti-parallel planar Schottky diodes as active nonlinear components are proposed. The input excitation is in V-band i.e. 56GHz and the output of the device is based on the third harmonic of each stage. The diodes are modeled and accurately matched their embedding impedances to the input and output lines to reach acceptable THz power levels at the targeted frequencies. The device is integrated with a low-loss and a low-cost all-silicon integrated technology and compared the advantages over the existing technologies such as reduced height metallic split-blocks and dielectric silicon-on-glass (SOG) integrated circuit technology.
In the proposed technology, all connections and passive components are made of the high-resistivity silicon substrate using bandgap periodic structures to achieve electromagnetic modal confinement. In addition, the designed integrated system is built on a single wafer with an accurately tuned high-precision and low-cost three-mask microfabrication process. Furthermore, the passive components, e.g. the filters, the power combiners, and the transitions between the silicon waveguides and the chip connections through planar metallic waveguides are designed for each multiplier stage starting from the millimeter wave, V-band, up to the terahertz wave.
The test setup for each stage of the device is proposed in addition to the fully integrated source design. The method of excitation is using contactless silicon probes made in-house for on-wafer probing of the devices. Different matching transitions are designed to couple the dielectric waveguide mode of the probe to silicon waveguides and conventional metallic transmission lines e.g., coplanar waveguides (CPW), coplanar striplines (CPS), and microstrip lines (MS) at different frequency bands up to the THz. The performance of the laser-machined silicon probes is suitable for all conducted experiments; however, the assembly and packaging of the probes are significantly complicated processes at THz frequencies due to the miniaturized dimensions.
Therefore, a new version of self-packaged silicon probes is designed, fabricated, and measured successfully. The new probe is used in the THz measurements.
Based on the simulations and measured data, the passives showed high performance with the proposed integration technology and were successfully used to build the first prototype of the THz source. A -1dBm generates power at 168GHz when excited with the 56GHz input signal to the first stage and ~ -4dBm at 0.5THz when directly excited with an input of 168GHz signal to the second stage; however, the output power level of the first stage was not enough to pump the second stage. Therefore, new designs based on two combined signal branches are fabricated and could improve the output power of the cascaded chain to ~ -14dBm at 0.5THz.
Finally, a system packaging technique is discussed that maintains the performance of the silicon-integrated system and achieves the mechanical and thermal practical requirements.