Browsing by Author "Chen, Peiyu"

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    An Integrated Germanium-Based THz Impulse Radiator with an Optical Waveguide Coupled Photoconductive Switch in Silicon
    (MDPI, 2019) Chen, Peiyu; Hosseini, Mostafa; Babakhani, Aydin
    This paper presents an integrated germanium (Ge)-based THz impulse radiator with an optical waveguide coupled photoconductive switch in a low-cost silicon-on-insulator (SOI) process. This process provides a Ge thin film, which is used as photoconductive material. To generate short THz impulses, N++ implant is added to the Ge thin film to reduce its photo-carrier lifetime to sub-picosecond for faster transient response. A bow-tie antenna is designed and connected to the photoconductive switch for radiation. To improve radiation efficiency, a silicon lens is attached to the substrate-side of the chip. This design features an optical-waveguide-enabled “horizontal” coupling mechanism between the optical excitation signal and the photoconductive switch. The THz emitter prototype works with 1550 nm femtosecond lasers. The radiated THz impulses achieve a full-width at half maximum (FWHM) of 1.14 ps and a bandwidth of 1.5 THz. The average radiated power is 0.337 μ W. Compared with conventional THz photoconductive antennas (PCAs), this design exhibits several advantages: First, it uses silicon-based technology, which reduces the fabrication cost; second, the excitation wavelength is 1550 nm, at which various low-cost laser sources operate; and third, in this design, the monolithic excitation mechanism between the excitation laser and the photoconductive switch enables on-chip programmable control of excitation signals for THz beam-steering.
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    Design Techniques and Measurement Methods for Broadband Millimeter-Wave and THz Systems in Silicon
    (2018-03-30) Chen, Peiyu; Babakhani, Aydin
    Short impulses in millimeter-wave (mm-wave) and THz regimes (30 GHz - 30 THz) have a potentially large bandwidth that can be exploited for various applications, for example, high-resolution 3D imaging, high-speed wireless communication, broadband spectroscopy, etc. Existing methods for impulse generation have the following drawbacks: First, photonics solutions are usually not compatible with silicon technologies, i.e. CMOS and BiCMOS, impeding higher level SOC designs; Second, electronic oscillator-based solutions usually require phase-locked loop (PLL) and delay-locked loop (DLL) to ensure coherency of generated impulses, which increases system complexity, power consumption, and die area; Third, electronics digital-to-impulse solutions can be further improved by generating shorter impulses, reducing late-time ringing, and achieving amplitude modulation. In addition, high demands on using silicon technology to generate picosecond or sub-picosecond impulses impose challenges on standard chip characterization methods in both time domain and frequency domain. This dissertation demonstrates three chip designs and one chip characterization method to resolve the aforementioned drawbacks and challenges. The first chip design is to use a CMOS-compatible silicon photonics process technology to design a THz PCA chip, which can radiate 1.14 ps impulses. The prototype silicon photonics chip enables easier integrations with other photonics and electronics devices on a single chip. The second chip design is to implement an asymmetric-VCO-based impulse radiator without requiring any PLL or DLL in a 130 nm SiGe BiCMOS. With on-chip antennas, it radiates 60 ps impulses with less power consumption, system complexity, and die area than conventional oscillator-based solutions. The designed impulse radiator has also been applied for 3D imaging. The last chip design is to apply a new circuit technique, nonlinear Q-switching impedance, to implement a 4 ps impulse radiator with pulse amplitude modulation in a 130 nm SiGe BiCMOS. An optoelectronics-based time-domain characterization method was invented to test the 4 ps impulse radiator, and this new measurement technique shows a significant accuracy improvement compared with standard time-domain methods. The demonstrated techniques in this dissertation show that silicon technology is a promising solution to generating picosecond and even sub-picosecond impulses and it is approaching to the performance of photonics devices. Ultra-broadband silicon-based impulse radiators can be characterized using optoelectronics technology to achieve better measurement accuracy.
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    High efficiency carbon nanotube thread antennas
    (AIP Publishing, 2017) Bengio, E. Amram; Senic, Damir; Taylor, Lauren W.; Tsentalovich, Dmitri E.; Chen, Peiyu; Holloway, Christopher L.; Babakhani, Aydin; Long, Christian J.; Novotny, David R.; Booth, James C.; Orloff, Nathan D.; Pasquali, Matteo
    Although previous research has explored the underlying theory of high-frequency behavior of carbon nanotubes (CNTs) and CNT bundles for antennas, there is a gap in the literature for direct experimental measurements of radiation efficiency. These measurements are crucial for any practical application of CNT materials in wireless communication. In this letter, we report a measurement technique to accurately characterize the radiation efficiency of λ/4 monopole antennas made from the CNT thread. We measure the highest absolute values of radiation efficiency for CNT antennas of any type, matching that of copper wire. To capture the weight savings, we propose a specific radiation efficiency metric and show that these CNT antennas exceed copper's performance by over an order of magnitude at 1 GHz and 2.4 GHz. We also report direct experimental observation that, contrary to metals, the radiation efficiency of the CNT thread improves significantly at higher frequencies. These results pave the way for practical applications of CNT thread antennas, particularly in the aerospace and wearable electronics industries where weight saving is a priority.
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    High-resolution Millimeter-wave Impulse-based MIMO 3D Imaging Radar in Silicon
    (2015-04-22) Chen, Peiyu; Babakhani, Aydin; Aazhang, Behnaam; Knightly, Edward W; Kono, Junichiro
    The research on millimeter-wave (mm-wave) silicon-based integrated 3D imaging radar has gained tremendous attention in academia over the past decade. Compared with conventional 2D imaging, 3D imaging captures both 1D depth information and 2D intensity maps. Impulse-based 3D imaging radar can also obtains more constitutional information of objects, like spectroscopy, so as to potentially have material identification functionality with 3D imaging simultaneously. The main objectives in the roadmapping of silicon integrated 3D imaging radar are higher image resolution, a larger image range and shorter acquisition time. With the dramatically improved performance of silicon transistors, mm-wave circuits using CMOS and BiCMOS technologies can generate picosecond-level impulses but with small RF power. Shorter impulses provide higher image resolution, but small RF power limits image range. Spatially coherent impulse combining from multiple silicon circuits is the solution to this problem. Compared with narrow-band phased-arrays that perform only 2D spatial filtering and have range-ambiguity problems, impulse-radiating arrays are capable of performing 3D spatial filtering that enhances the imaging sensitivity of a certain point in 3D space without sacrificing image resolution. Therefore, impulse-based MIMO imaging radar can achieve both high resolution and a large image range simultaneously. In this present work, a 60ps impulse radiator with an on-chip antenna is implemented in the IBM 130nm SiGe BiCMOS process technology. The impulse radiator is the core element of the synthetic arrays that are used to perform 3D imaging in this thesis. A pulsed-VCO-based architecture is designed based on an asymmetric cross-coupled pulsed VCO to convert a digital input signal to radiated impulses. The deliberate asymmetry in the pulsed VCO is introduced to minimize the timing jitter of the radiated impulses in order to achieve spatially coherent impulse combining with high efficiency. The radiated impulses have a record RMS jitter of 178fs with 64 averaging when the input trigger signal has a RMS jitter of 150fs. Two widely spaced impulse radiators are used to perform spatially coherent impulse combining with an efficiency of 98.7%. As the first step in demonstrating impulse-based MIMO 3D imaging radar, in this work, custom synthetic array imaging systems were built based on the proposed silicon-based integrated impulse radiator. 3D imaging of metallic and dielectric objects (rocks immersed in oil) have been performed successfully. A depth accuracy of 27um, a depth resolution of 9mm and a lateral resolution of 8mm at 10cm distance in the air have been achieved. To the author’s knowledge, this work demonstrates the first high-resolution 3D images that are generated by using synthetic array imaging systems based on a fully-integrated impulse radiator in silicon. Future work includes implementing fully integrated impulse transceivers and fully integrated impulse-based MIMO 3D imaging radar with independent time-delay controls.
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    Modulation-Doped Multiple Quantum Wells of Aligned Single-Wall Carbon Nanotubes
    (Wiley, 2017) Komatsu, Natsumi; Gao, Weilu; Chen, Peiyu; Guo, Cheng; Babakhani, Aydin; Kono, Junichiro
    Heterojunctions, quantum wells, and superlattices with precise doping profiles are behind today's electronic and photonic devices based on III–V compound semiconductors such as GaAs. Currently, there is considerable interest in constructing similar artificial 3D architectures with tailored electrical and optical properties by using van der Waals junctions of low-dimensional materials. In this study, the authors have fabricated a novel structure consisting of multiple thin (≈20 nm) layers of aligned single-wall carbon nanotubes with dopants inserted between the layers. This “modulation-doped” multiple-quantum-well structure acts as a terahertz polarizer with an ultra-broadband working frequency range (from ≈0.2 to ≈200 THz), a high extinction ratio (20 dB from ≈0.2 to 1 THz), and a low insertion loss (<2.5 dB from ≈0.2 to 200 THz). The individual carbon nanotube films—highly aligned, densely packed, and large (2 in. in diameter)—were produced using vacuum filtration and then stacked together in the presence of dopants. This simple, robust, and cost-effective method is applicable to the fabrication of a variety of devices relying on macroscopically 1D properties of aligned carbon nanotube assemblies.