Scaling Issues in Trigate GaN Nanowire Transistors
Date Issued
2012
Date
2012
Author(s)
Chen, Chin-Yi
Abstract
This thesis analyzes the scalability of nitride-based nanowire high electron mobility transistors (HEMTs). The positive polarization charge between the AlGaN and GaN interface induces high density of electron which also known as the two dimensional electron gate (2DEG). With the 2DEG, the device does not need high n-type doping to increase the electron density in the channel. Therefore, the mobility can reach a high value due to less impurity scattering in the device. We use a fully three dimensional(3D) self-consistent nite element model to solves drift-di usion and Poisson equations and obtains the electrical properties in the device with 3D structure. In the scaling issue of Si-based transistors, the structure of silicon on insulator(SOI)
and the FINFET are two common ways to suppress the short channel
e ect (SCE). In the GaN-based transistor, AlGaN and AlInN back
barrier, similar to the structure of SOI, can suppress the SCE. How-
ever, the negative polarization charge at the interface of the GaN
channel and the back barrier reduces the saturation current.
In this thesis, we discuss the GaN-HEMT in a 3D tri-gate struc-
ture, which is similar to the structure of FINFET. The I-V curve,
vtransconductance (gm), sub-threshold swing, and drain induce barrier
lowering, fT are discussed.
The tri-gate structure can well suppress the SCE when the wire
width is reduced. However, the fT decreases at the same time due to
the e ect of the lateral gate. To optimize this tri-gate structure, we
replace the AlGaN top insulator with AlInN to increase the 2DEG in
the channel.
Furthermore, we reduce the distance between drain and source to
reduce the channel resistance. With a smaller channel resistance in the
channel, a higher fT can be obtained. In sum, the optimize structure
can suppress the SCE without sacri cing the fT .
Subjects
GaN
high electron mobility transistor
short channel effect
Type
thesis
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