Download Advanced materials and device structures for nonvolatile magnetic memory applications.

NUS Graduate School for Integrative Sciences and Engineering
Research Project Write-up
Title of Project : Advanced materials and device structures for nonvolatile
magnetic memory applications
Name of Supervisor : Teo Kie Leong
Contact Details:
Dept. of Electrical & Computer Engineering
National University of Singapore
4 Engineering Drive 3
Singapore 117576
Phone: (+65)6516-4543
Fax: (+65)6779-1103
Office: E2-03-30
E-mail: [email protected]
Short Description
Magnetic random access memory (MRAM) has been envisaged to have the capability
of the speed of static RAM and the density of dynamic RAM, and is nonvolatile. It
could be the “dream memory” since it has the potential to replace all the existing
memory devices in a computer, maybe even the hard disk drives, becoming the
“universal memory”. MRAM used sub-micron magnetic tunnel junction and the
process integration is compatible with standard CMOS allowing it to be easily
embedded in System-on-Chip applications. Because the data is stored as a magnetic
state, MRAM is inherently nonvolatile as well as having unlimited endurance and fast
operation. The project involves the fabrication of epitaxial Heusler-alloys-based and
perpendicular MTJ for spin-torque MRAM (ST-MRAM) and investigates their spindependent properties such as tunneling magneto-resistance (TMR) and currentinduced magnetization switching (CIMS). Our ultra-high vacuum deposition cluster
tool (UHV-CDT) will be a dedicated backbone to fabricate novel TMR device
structures with high MR ratio. The UHV cluster tool allows growth of perfect
crystalline structure and atomically sharp interfaces which enable discovery of new
material systems with coherent tunneling, control of interface strain and spin
dependent tunneling, low defect density and greater device uniformity.
Title of Project : Dilute magnetic semiconductors for spintronic applications
Supervisor : Teo Kie Leong
Contact Details:
Dept. of Electrical & Computer Engineering
National University of Singapore
4 Engineering Drive 3
Singapore 117576
Phone: (+65)6516-4543
Fax: (+65)6779-1103
Office: E2-03-30
E-mail: [email protected]
Short Description
The field of dilute magnetic semiconductors (DMS) is currently one of intense
activity. These materials are of great interest because of the novelty of their
fundamental properties and also due to their potential as the basis of future
semiconductor spintronic technologies which promise integration of magnetic,
semiconducting and optical properties and a combination of information processing
and storage functionalities. They should be compatible with existing microelectronic
technologies and have potential as low-dissipation, non-volatile, and nano-scale
alternatives to current microelectronics. The project involves molecular beam epitaxy
(MBE) growth of DMS materials, characterization, and electrical transport studies.
Thin films and spintronic prototype devices, such as the spin-filters will be fabricated
to investigate the spin injection efficiency and transport of spin-polaized current in
semiconductor using different injector materials (spin sources), spin transfer
interfaces or aligners and nanostructures.
Title of Project : Gallium Nitride-based materials for high power electronic
applications
Name of Supervisor : Teo Kie Leong
Contact Details:
Dept. of Electrical & Computer Engineering
National University of Singapore
4 Engineering Drive 3
Singapore 117576
Phone: (+65)6516-4543
Fax: (+65)6779-1103
Office: E2-03-30
E-mail: [email protected]
Short Description
GaN-based materials have superior properties, such as large critical electric field,
wide energy band gap EG, and high electron mobility, making them advantageous as
materials of choice for high power, high frequency, and high temperature
applications. High electron mobility transistors (HEMTs) employing the AlGaN/GaN
heterostructure further exploit the high electron mobility in the two-dimensional
electron gas (2-DEG) at the AlGaN/GaN interface. Nonetheless, there are still many
issues needed to be solved. Many GaN-based HEMTs employ a Schottky gate which
has the shortcoming of a large gate leakage current density JG. In addition, GaN
HEMTs suffer from current collapse during large signal operation at high frequency,
usually referred as “dc-to-radio frequency (RF) dispersion”. Enhancement mode
HEMTs with a positive threshold voltage VTH are desirable for many circuit
applications. The VTH of HEMTs depends on the epitaxial structure design as well as
surface states.
The project involves the design and fabrication of GaN-based high-power HEMTs
and focus on several key process modules, some of which are limiting factors for
achieving better electrical performance. This includes surface/interface quality,
device passivation and encapsulation for operation under harsh environment (high
temperature and harsh chemical environment). All process modules will be integrated
in GaN high-power devices. Additionally, we will investigate the device physics
which involves modeling and simulation work as well as study the carrier transport
and scattering mechanisms in the two-dimensional electron gas (2DEG) channel for
the novel AlGaN/GaN HEMT using magneto-transport measurement techniques.
Title of Project: Solid-state Lighting and Displays.
Name of Supervisor : Teo Kie Leong
Contact Details:
Dept. of Electrical & Computer Engineering
National University of Singapore
4 Engineering Drive 3
Singapore 117576
Phone: (+65)6516-4543
Fax: (+65)6779-1103
Office: E2-03-30
E-mail: [email protected]
Short Description
Today the mainstream solid-state lighting (SSL) still relies on inorganic
semiconductor technology; for example, InGaN/GaN quantum well (QW) based LED
plus phosphors. III-nitride based LEDs critically require high crystal quality of the
epitaxial layers, and therefore are not satisfactory for general lighting in terms of both
price and efficiency. We intend to address this problem by adopting a new strategy
that makes use of excitonic emission in different low dimensional semiconductors
(LDS) such as 2D-QWs, 1D-nanowires (NWs, or quantum wires) and 0 D-nanocrystal
quantum dots (QDs). All these low dimensional semiconductor structures (LDSS)
serve as basic building blocks for light emitting devices, but possess different
characteristics. We will make use of the distinctive characteristics of these LDS
to design and demonstrate new device structures and therefore achieve device
performance previously unattainable. The project involves design and fabrication of
alternative excitonic architectures for LED applications with higher
performance/cost ratio, study the fundamental physics underlying the excitonic
energy transfer between different component materials and improvement of energy
efficiency and spectral quality of LEDs by taking advantage of different
characteristics of inorganic QWs, NWs and QDs.