Post Graduate Activities
Student: Durga Gao
Project title: Optimization of germanium based MOSFET fabrication processes
For the scaling of silicon CMOS technology down to the 90 nm node, researchers scaled feature sizes such as gate length, gate oxide thickness, depletion width, and the supply voltage. Scaling beyond the 90 nm node, structural changes to the planar technology were required or the replacement the silicon with a high mobility semiconductor. Belongs to the same group in the periodic table as silicon, germanium is having approximately four times higher electron mobility and two times higher hole mobility compared with silicon. For scaled MOSFET fabrication, this high mobility is a great advantage. The smaller band gap of germanium (0.66 eV) broadens the optical absorption spectrum for telecommunication applications. Its low melting point allows fabrication of germanium MOSFET with a considerably lower thermal budget compared with silicon MOSFETs.
Nickel germanide Schottky contacts were realized on n-type germanium with an optimum Schottky barrier height value of 0.68 eV and an implant-less fabrication process is developed at low thermal budget with nickel germanide based source/drain Schottky contacts for germanium p-channel MOSFETs. De-pinning of the Fermi level for aluminium contacts to n-type germanium is developed by introducing a thin layer of atomic layer deposited (ALD) alumina (Al2O3) and hafnium di oxide (HfO2). A 25 Å thick alumina interfacial can successfully un-pin the Fermi-level pinning of aluminium contacts on n-germanium by reducing the barrier height from ~0.7 eV for aluminium contact on n-germanium to 0.3 eV by optimizing series resistance and ideality factor.
Student: Teng Hwang Tan
Project Title: Silicon piezoresistors for MEMS pressure sensor applications
Is currently working towards his PhD in MEMS pressure sensor at Queens University Belfast, UK. Silicon based micromachining technology enables the realization of high performance microelectromechanical systems (MEMS) including a range of physical and environmental sensors. Pressure sensors are used for a wide range of monitoring and control applications, e.g. environmental, industrial, aircraft, automotive. Micromachined pressure sensors are used at present, but require further research to improve their performance in terms of size, power consumption and manufacturing cost. His recent researches focus on reviewing pressure sensor technology and new development in the area."
Project Title: Single crystal Ge on SiO2 using rapid melt process.
Germanium is a suitable material for high performance infra-red (IR) photovoltaic devices. Thin-films of germanium can be used to reduce the complexity and expense of existence energy conversion devices. Germanium on insulator (GeOI) is seen potential structural for thin-film photovoltaic application. High-quality, single crystal, GeOI structures can be produced by a Rapid Melt Growth (RMG) process. Initial experiments on silicon substrates have shown germanium thin-films by RMG at high temperature have Raman intensity approximately 299.5 cm-1. The peak position is shifted slightly indicating small tensile stress, which is due to differences in thermal expansion coefficients of the materials. The full width half maximum (FWHM) of 3.3 for germanium films produced by RMG indicates good crystalline quality comparable with bulk germanium (FWHM 3.2) and thus the potential to produce low cost, high quality future solar cells.
Student: Yao Wang
Mr Yao Wang is pursuing his PhD degree in the area MOSFET sensors for microcantilever. The research focuses on stress changes and enhancements on cantilever structure surface for basic pressure, environmental and biomedical applications. It involves a thorough review of present cantilever based sensor technology, including detection methods for deflection and stress concentration. Surface and bulk micromachining techniques are essential to fabricate the devices, and the cantilever surface can be then functionalised to selectively bind target substances.