VLSI physical design, the process that converts circuit schematics to manufacturable layouts in an automatic fashion, consists of many long-lasting and challenging problems that have been solved by sub-optimal algorithms over the decades. As the technology scaling advances, the sub-optimality becomes more severe and problematic. Machine learning (ML) is one of the promising solutions that help designers achieve the desired Power, Performance, and Area (PPA) goals. In this talk, we present our recent works on utilizing ML algorithms to improve various stages of the modern physical design flow. They span from partitioning, placement, routing, and timing optimization, where Reinforcement, Transformer, Adversarial, and Graph Learning are adopted. We also showcase our recent work recognized with the best paper award from the ACM Design Automation Conference in 2023.

 In this Seminar, Various Packaging researches such as high performance system design, a novel simulation tool development, and hardware security analysis/design will be delivered. Also, an important role of packaging technologies in the era of mobility requiring low noise, low power, and ultra-low latency will be emphasized. 

In the last few decades, there has been increasing interest and investment in developing advances in analysis equipment to study the nervous system. The aim of neuroscientific studies is to explain the function of a neural circuit which is a population of neurons interconnected by synapses. Currently, two-photon fluorescence microscopy is widely used. However, this equipment requires expensive and huge implementations such as precise alignments and lenses, in general. In addition, it is necessary to carry out a pretreatment, like the fluorescent labeling of biomolecules in samples. To overcome these limitations, we proposed a bio-image sensor that not only is a portable and customizable device but also has potential in implantation for long-term recording. In order to image spatiotemporal activities of different neurotransmitters simultaneously, this sensor has been designed to consist of an enzyme-immobilized ISFET array and an integrated readout circuit. The details of the sensor and its future application will be given in this talk.

This seminar will first introduce the research environments of France focusing on French governmental research organizations such as CNRS, INSERM, CEA, INRA etc. The system of CNRS, the largest research institute of France, will be explained with its history and highlights. Research topic of CNRS researchers is important to begin their career and thus an example will be shortly introduced. Secondly, research activities on heterogeneous integration for wireless sensor network will be summarized. Powering sensor nodes based on external vibration is interesting to make them energically autonomous. As a method of energy harvesting, extraction of electrical energy using a vibrating piezoelectric device is being attractive. Other energy harvesting devices will be also presented.

Sub-terahertz and terahertz waves, electromagnetic waves within the frequency range from 100GHz to 10THz, enable unprecedented capabilities thanks to their unique characteristics, such as short wavelength, wide bandwidth and spectral specificity. Key applications include high-resolution imaging, high-speed data communication and gas analysis with absolute specificity through rotational spectroscopy. However, the high cost of the terahertz instrumentation has been limiting its proliferation. If developed, compact and low-cost terahertz electronic systems will accelerate the adoption of terahertz technologies in everyday life. Si-based terahertz electronics can be one of the key enabler of such systems.

In this seminar, Si CMOS integrated circuits for terahertz applications will be introduced. Following a brief discussion on the tradeoffs and design approaches for CMOS terahertz circuit design, details of example circuits will be presented. The example circuits include 1) a 410-GHz short-range imaging receiver 2) a 240-GHz wideband receiver for rotational spectroscopy 3) a 300-GHz QPSK transmitter for 30-Gbps dielectric waveguide communications.

MEMS technologies have enabled many innovative applications across various disciplines. In this talk, recent developments of MEMS-enabled implantable biomedical micro devices, liquid metal microfluidics and nanophotonics developed at UT Dallas will be presented. Examples of the implantable micro devices include a fully-integrated inductively-coupled battery-less wireless pressure sensor for intraocular pressure sensing application, a fully-integrated inductively-coupled wireless micro neurostimulator forchronic pain management, and a micro cell container for β-cell transplantation for diabetes treatment. For the liquid metal microfluidics, fundamental studies on the microfluidic platforms for liquid metal manipulation and its enormous potential along with wide range of applications will be discussed. Nanophotonics is an emerging field of study which deals with interaction of light with nano scale matters. While there have been many fascinating demonstrations in nanophotonics, adding on-demand tunability to the nanophotonics would greatly expand existing application areas and potentially enable unforeseen new applications. Among many exciting “tunable” nanophotonics, this talk gives a review about recent developments of tunable nano photonic devices using MEMS.

Conventional image sensors achieve color imaging using absorptive organic dye filters. These face considerable challenges however in the trend toward ever higher pixel densities and advanced imaging such as multispectral imaging and polarization-resolved imaging. In this talk, we will present a new paradigm for color imaging based on all-silicon nanowire devices without any color filters. We fabricate pixels consisting of vertical silicon nanowires with integrated photodetectors, demonstrate that t heir spectral sensitivities are governed by nanowire radius, and perform color imaging. We also demonstrate polarization-resolving photodetectors consisting of silicon nanowires with elliptical cross sections. Our approach is conceptually different from filter-based methods, as absorbed light is converted to photocurrent, ultimately presenting the opportunity for very high photon efficiency. This work was performed at Harvard University under the supervision of Prof. Kenneth B. Crozier.

Quantum dot
lasers epitaxially grown on Si are promising for an efficient light source for
silicon photonics. In the talk, I will present record-high performance and
excellent reliability of 1.3 μm quantum dot lasers on Si enabled by a low
threading dislocation density GaAs buffer layer. Continuous-wave threshold
currents as low as 4.8 mA and output powers of 185 mw have been achieved from
narrow ridge-waveguide lasers at 20 °C. P-modulation doped lasers operated up
to 107 °C. 1800-hour reliability tests at 35 °C showed an extrapolated
mean-time-to-failure of more than a million hours. Micro-ring QD lasers on Si
were also fabricated and showed an ultralow threshold current of 0.5 mA. I will
also present a preliminary result on monolithically integrated III/V laser,
waveguide, and photodetectors on Si. This represents a significant stride
toward efficient, scalable, and reliable III-V lasers on on-axis Si substrates for
photonic integrate circuits that are fully compatible with CMOS foundries.

III-nitride laser diodes (LDs) have been developed for many applications such as optical storage, medical, and solid-state lighting. However, the performance of LDs grown on conventional polar (0001) c-plane GaN has been hindered due to polarization-induced electric fields, leading to a reduction of wave-function overlap. Recent progress on semipolar and nonpolar planes has shown significant improvement in high-power performance of LEDs and LDs by reducing the polarization-induced electric field. Conventional III-nitride LEDs have typical bandwidth limits in the MHz range due to comparatively long carrier lifetime (on the order of ns) and significant RC parasitic effect. Even worse, for white lighting configuration, the response is significantly limited by slow relaxation lifetime (on the order of μs) of phosphor conversion. However, recent studies on LDs for light fidelity (LiFi) applications have demonstrated more than GHz bandwidth and Gbit/s data transmission rate with inherent advantage of short photon lifetime. As an alternative to LED technology, the use of laser diodes (LDs) as a transmitter presents a viable approach to overcome the limitations of modulation bandwidth as well as the lighting efficiency. Despite of these merits, only limited studies have been reported for LD-based VLC and LiFi demonstration without notable improvement in modulation capabilities. Since semipolar and nonpolar LDs are expected to have higher differential gain and lower threshold than c-plane LDs as mentioned above, they also have high potential for improvements in modulation bandwidth. Thus, nonpolar and semipolar LD is potential candidate for future LiFi applications requiring high-capacity for high-speed data transmission as well as high-efficiency for lighting.