Xu Li

Bio: Xu Li is an academic researcher from University of Glasgow. The author has contributed to research in topics: Etching (microfabrication) & MOSFET. The author has an hindex of 15, co-authored 77 publications receiving 1333 citations. Previous affiliations of Xu Li include Freescale Semiconductor.

The 2018 GaN power electronics roadmap

Abstract: Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

Enhancement-Mode GaAs MOSFETs With an $\hbox{In}_{0.3} \hbox{Ga}_{0.7}\hbox{As}$ Channel, a Mobility of Over 5000 $ \hbox{cm}^{2}/\hbox{V} \cdot \hbox{s}$ , and Transconductance of Over 475 $\mu\hbox{S}/\mu\hbox{m}$

Abstract: We present metal-gate high-k-dielectric enhancement-mode (e-mode) III-V MOSFETs with the highest reported effective mobility and transconductance to date. The devices employ a GaGdO high-k (k = 20) gate stack, a Pt gate, and a delta-doped InGaAs/AlGaAs/GaAs hetero-structure. Typical 1-mum gate length device figures of merit are given as follows: saturation drive current, Id,sat = 407 muA/mum; threshold voltage, Vt = +0.26 V; maximum extrinsic transconductance, gm = 477 muS/mum (the highest reported to date for a III-V MOSFET); gate leakage current, Ig = 30 pA; subthreshold swing, S = 102 mV/dec; on resistance, Ron = 1920 Omega-mum; Ion/Ioff ratio = 6.3 x 104; and output conductance, gd = 11 mS/mm. A peak electron mobility of 5230 cm2/V. s was extracted from low-drain-bias measurements of 20 mum long-channel devices, which, to the authors' best knowledge, is the highest mobility extracted from any e-mode MOSFET. These transport and device data are highly encouraging for future high-performance n-channel complementary metal-oxide-semiconductor solutions based on III-V MOSFETs.

Nanofabrication of high aspect ratio (∼50:1) sub-10 nm silicon nanowires using inductively coupled plasma etching

Abstract: The development of nanofabrication techniques for creating high aspect ratio (∼50:1) sub-10 nm silicon nanowires (SiNWs) with smooth, uniform, and straight vertical sidewalls using an inductively coupled plasma (ICP) etching process at 20 °C is reported. In particular, to improve the quality and flexibility of the pattern transfer process for high aspect ratio SiNWs, hydrogen silsesquioxane, a high-resolution, inorganic, negative-tone resist for electron-beam lithography has been used as both the resist for defining sub-10 nm patterns and the hard mask for etching the underneath silicon material. The effects of SF6/C4F8 gas flow rates, chamber pressure, platen power and ICP power on the etch rate, selectivity, and sidewall profile are investigated. To minimize plasma-induced sidewall damage, moderate plasma excitation power (ICP power of 600 W) and low ion energy (platen power of 6–12 W) were used. Using the optimized etch process at room temperature (20 °C), the authors have successfully fabricated sub-1...

High Mobility III-V MOSFETs For RF and Digital Applications

Abstract: Developments over the last 15 years in the areas of materials and devices have finally delivered competitive III-V MOSFETs with high mobility channels. This paper briefly reviews the above developments, discusses properties of the GdGaO/ Ga2O3 MOS systems, presents GaAs MOSFET DC and RF data, and concludes with an outlook for high indium content channel MOSFETs. GaAs based MOSFETs are potentially suitable for RF power amplification, switching, and front-end integration in mobile and wireless applications while MOSFETs with high indium content channels are of interest for future CMOS applications.

An Ultralow-Resistance Ultrashallow Metallic Source/Drain Contact Scheme for III–V NMOS

Abstract: We report an ultrashallow metallic source/drain (S/D) contact scheme for fully self-aligned III-V NMOS with specific contact resistivity and sheet resistance which, for the first time, demonstrate performance metrics that may be compatible with the ITRS Rext requirements for 12-nm technology generation device pitch. The record specific contact resistivity between the contact pad and metallic S/D of ρc = 2.7 ·10-9 Ω·cm2 has been demonstrated for 10 nm undoped InAs channels by forming an ultrashallow crystalline ternary NiInAs phase with Rsh = 97 Ω/sq for a junction depth of 7 nm. The junction depth of the S/D scheme is highly controllable and atomically abrupt.

Damascene copper electroplating for chip interconnections

Abstract: Damascene copper electroplating for on-chip interconnections, a process that we conceived and developed in the early 1990s, makes it possible to fill submicron trenches and vias with copper without creating a void or a seam and has thus proven superior to other technologies of copper deposition. We discuss here the relationship of additives in the plating bath to superfilling, the phenomenon that results in superconformal coverage, and we present a numerical model which accounts for the experimentally observed profile evolution of the plated metal.

The 2018 GaN power electronics roadmap

Abstract: Gallium nitride (GaN) is a compound semiconductor that has tremendous potential to facilitate economic growth in a semiconductor industry that is silicon-based and currently faced with diminishing returns of performance versus cost of investment. At a material level, its high electric field strength and electron mobility have already shown tremendous potential for high frequency communications and photonic applications. Advances in growth on commercially viable large area substrates are now at the point where power conversion applications of GaN are at the cusp of commercialisation. The future for building on the work described here in ways driven by specific challenges emerging from entirely new markets and applications is very exciting. This collection of GaN technology developments is therefore not itself a road map but a valuable collection of global state-of-the-art GaN research that will inform the next phase of the technology as market driven requirements evolve. First generation production devices are igniting large new markets and applications that can only be achieved using the advantages of higher speed, low specific resistivity and low saturation switching transistors. Major investments are being made by industrial companies in a wide variety of markets exploring the use of the technology in new circuit topologies, packaging solutions and system architectures that are required to achieve and optimise the system advantages offered by GaN transistors. It is this momentum that will drive priorities for the next stages of device research gathered here.

High transconductance organic electrochemical transistors.

Abstract: The development of transistors with high gain is essential for applications ranging from switching elements and drivers to transducers for chemical and biological sensing. Organic transistors have become well-established based on their distinct advantages, including ease of fabrication, synthetic freedom for chemical functionalization, and the ability to take on unique form factors. These devices, however, are largely viewed as belonging to the low-end of the performance spectrum. Here we present organic electrochemical transistors with a transconductance in the mS range, outperforming transistors from both traditional and emerging semiconductors. The transconductance of these devices remains fairly constant from DC up to a frequency of the order of 1 kHz, a value determined by the process of ion transport between the electrolyte and the channel. These devices, which continue to work even after being crumpled, are predicted to be highly relevant as transducers in biosensing applications.