G. P. Li

Bio: G. P. Li is an academic researcher from University of California, Irvine. The author has contributed to research in topics: Microelectromechanical systems & Microelectronics. The author has an hindex of 10, co-authored 47 publications receiving 287 citations.

Characterization and use of laser-based lysis for cell analysis on-chip

Abstract: We demonstrate the use of a pulsed laser microbeam for cell lysis followed by electrophoretic separation of cellular analytes in a microfluidic device. The influence of pulse energy and laser focal point within the microchannel on the threshold for plasma formation was measured. The thickness of the poly(dimethylsiloxane) (PDMS) layer through which the beam travelled was a critical determinant of the threshold energy. An effective optical path length, Leff ,f or the laser beam can be used to predict the threshold for optical breakdown at different microchannel locations. A key benefit of laser-based cell lysis is the very limited zone (less than 5 mm) of lysis. A second asset is the rapid cell lysis times (approx. microseconds). These features enable two analytes, fluorescein and Oregon Green, from a cell to be electrophoretically separated in the channel in which cell lysis occurred. The resolution and efficiency of the separation of the cellular analytes are similar to those of standards demonstrating the feasibility of using a pulsed laser microbeam in single-cell analysis.

A reconfigurable spiral antenna for adaptive MIMO systems

Abstract: We present a reconfigurable spiral antenna for use in adaptive MIMO systems. The antenna is capable of changing the sense of polarization of the radiated field. It is fabricated by using an RF-MEMS technology compatible with microwave laminate substrates developed within the author's group. The proposed antenna structure is built on a number of rectangular-shaped bent metallic strips interconnected to each other with RF-MEMS actuators. Two senses of polarization, RHCP and LHCP, are achieved by configuring the physical structure of the antenna, that is, by changing the winding sense of the spiral, through judicious activation of MEM actuators. The fabrication process for the monolithic integration of MEM actuators with bent microstrip pixels on RO4003-FR4 microwave laminate substrate is described. The measured and calculated radiation and impedance characteristics of the antenna are given. The operating frequency of the presented antenna design can easily be adjusted to be compatible with popular IEEE networking standards such as 802.11a.

Fast-lysis cell traps for chemical cytometry

Abstract: Electrically addressable cell traps were integrated with capillary electrophoresis for the analysis of the contents of single adherent cells. Electrodes composed of indium tin oxide were patterned on a glass surface followed by formation of topographical cell traps using 1002F photoresist. Single cells trapped in the holes could be lysed in less than 66 ms by applying a brief electric field (10 ms) across the electrode beneath the cell and the ground electrode placed in the aqueous media above the cell traps. The gas formed during cell lysis remained localized within the cavity formed by the 1002F photoresist. The retention of the gas in the cell trap enabled the cell traps to be coupled to an overlying capillary without blockage of the capillary. Single cells cultured in the traps were loaded with fluorescein and Oregon Green and then electrically lysed. By simultaneous application of an electric field to the capillary, the cell's contents were loaded into the capillary and electrophoretically separated. Orgeon Green and fluorescein from a single cell were fully resolved in less than two minutes. The use of a single patterned electrode beneath the 1002F cell trap yielded a simple easily fabricated design that was robust when immersed in aqueous solutions. Moreover, the design can easily be scaled up to create arrays of adherent cells for serial analyses using a single capillary or for parallel analysis by mating to an array of capillaries. Enhancing the rate of analysis of single adherent cells would enable a greater understanding of cellular physiology.

Resolving the mechanisms of current gain increase under forward current stress in poly emitter n-p-n transistors

Abstract: The mechanisms behind moderate bias current gain ( beta ) increase of n-p-n transistors under forward current stress are investigated in polysilicon emitter transistors processed with different dopant impurities and concentrations, and with different amounts of hydrogen plasma treatment. The results suggest that transport of atomic hydrogen toward the poly/monosilicon interface region and its subsequent passivation of dangling bonds at both poly grain boundaries and the poly/monosilicon interface are responsible for the moderate bias beta increase. To alleviate the beta instability, elimination of hydrogen involvement and/or a higher doping concentration inside the poly emitter in the back-end-of-line (BEOL) processes are/is recommended. >

High-Power Magnetically Actuated Microswitches Fabricated in Laminates

Abstract: We report on a microelectromechanical magnetic dc switch that operates at low control voltage (3 V), magnetically latches at on/off stage, and switches large voltages and currents, both dc and ac, in under 3 ms. The device, which measures 3 mm t 3 mm fully packaged, has been measured to handle 0.97 A at 10.6 Vdc (10.2 W) and 15 W at 110 Vac. This represents a remarkable power-handling capability for such a small device, which is almost impossible to achieve in conventional microelectromechanical system devices. The device is constructed using laminate MEMS technology, which is fully compatible with large-scale manufacturing by advanced microelectronics packaging manufacturers. This device has important applications in electronic switching applications for dc circuits, ac circuits, and, potentially, for RF circuits.

SiGe HBT technology: a new contender for Si-based RF and microwave circuit applications

Abstract: The silicon-germanium heterojunction bipolar transistor (SiGe HBT) is the first practical bandgap-engineered device to be realized in silicon. SiGe HBT technology combines transistor performance competitive with III-V technologies with the processing maturity, integration levels, yield, and hence, cost commonly associated with conventional Si fabrication. In the ten-and-one-half years since the first demonstration of a functional transistor, SiGe HBT technology has emerged from the research laboratory, entered manufacturing on 200-mm wafers, and is poised to enter the commercial RF and microwave market. State-of-the-art SiGe HBT's can deliver: (1) f/sub T/ in excess of 50 GHz; (2) f/sub max/ in excess of 70 GHz; (3) minimum noise figure below 0.7 dB at 2.0 GHz; (4) 1/f noise corner frequencies below 500 Hz; (5) cryogenic operation; (6) excellent radiation hardness; (7) competitive power amplifiers; and (8) reliability comparable to Si. A host of record-setting digital, analog, RF, and microwave circuits have been demonstrated in the past several years using SiGe HBT's, and recent work on passives and transmission lines on Si suggest a migratory path to Si-based monolithic microwave integrated circuits (MMIC's) is possible. The combination of SiGe HBT's with advanced Si CMOS to form an SiGe BiCMOS technology represents a unique opportunity for Si-based RF system-on-a-chip solutions. This paper reviews state-of-the-art SiGe HBT technology and assesses its potential for current and future RF and microwave systems.

25th anniversary article: carbon nanotube- and graphene-based transparent conductive films for optoelectronic devices.

Abstract: Carbon nanotube (CNT)- and graphene (G)-based transparent conductive films (TCFs) are two promising alternatives for commonly-used indium tin oxide-based TCFs for future flexible optoelectronic devices. This review comprehensively summarizes recent progress in the fabrication, properties, modification, patterning, and integration of CNT- and G-TCFs into optoelectronic devices. Their potential applications and challenges in optoelectronic devices, such as organic photovoltaic cells, organic light emitting diodes and touch panels, are discussed in detail. More importantly, their key characteristics and advantages for use in these devices are compared. Despite many challenges, CNT- and G-TCFs have demonstrated great potential in various optoelectronic devices and have already been used for some products like touch panels of smartphones. This illustrates the significant opportunities for the industrial use of CNTs and graphene, and hence pushes nanoscience and nanotechnology one step towards practical applications.

Design and Evaluation of a Reconfigurable Antenna Array for MIMO Systems

Abstract: New reconfigurable antenna array is demonstrated for multiple input multiple output (MIMO) communication systems that improves link capacity in closely spaced antenna arrays. The antenna system consists of an array of two printed dipoles separated by a distance of a quarter wavelength. Each of the dipoles can be reconfigured in length using PIN diode switches. The switch configuration can be modified in a manner adaptive to changes in the environment. The configuration of switches effects the mutual coupling between the array elements, and subsequently, the radiation pattern of each antenna, leading to different degrees of pattern diversity which can be used to improve link capacity. The PIN diode-based reconfigurable antenna solution is first motivated through a capacity analysis of the antenna in a clustered MIMO channel model. A new definition of spatial correlation coefficient is introduced to include the effects of antenna mismatch and radiation efficiency when quantifying the benefit of pattern diversity. Next, the widespread applicability of the proposed technique is demonstrated, relative to conventional half wavelength printed dipoles, using computational electromagnetic simulation in an outdoor and indoor environment and field measurements in an indoor laboratory environment. It is shown for the 2 times 2 system considered in this paper, that an average improvement of 10% and 8% is achieved in link capacity for a signal to noise ratio (SNR) respectively of 10 dB and 20 dB in an indoor environment compared to a system employing non reconfigurable antenna arrays.

Chemical Analysis of Single Cells

Abstract: In this Review, we provide an overview of methods developed for chemical analysis of single cells over the last two years. Many biological systems contain an ensemble of cells with heterogeneous chemistry; therefore, it is important to analyze them on an individual basis in order to elucidate the role each cell plays in the function of these systems. In clinical diagnostics, the development of extremely sensitive measurements, down to single cells, may provide the best ability for diagnoses. Single cell analysis has, in fact, been present for quite some time. Investigators in life sciences consider the cell as the unit of life and so the pursuit to quantify, image, and modulate the cell has been ongoing for decades.

Compositions and methods for sample processing

Abstract: This disclosure provides methods and compositions for sample processing, particularly for sequencing applications. Included within this disclosure are bead compositions, such as diverse libraries of beads attached to large numbers of oligonucleotides containing barcodes. Often, the beads provides herein are degradable. For example, they may contain disulfide bonds that are susceptible to reducing agents. The methods provided herein include methods of making libraries of barcoded beads as well as methods of combining the beads with a sample, such as by using a microfluidic device.