<p>Beta-gallium oxide (<i>β</i>-Ga<sub>2</sub>O<sub>3</sub>) is an emerging wide bandgap semiconductor for
next generation power devices which offers the potential to replace GaN and
SiC. It has an ultra-wide bandgap (UWBG) of 4.8 eV and a corresponding <i>E</i><sub>br </sub>of 8 MV/cm. <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>also possesses a decent intrinsic electron mobility limit of 250
cm<sup>2</sup>/V<i>·</i>s, yielding high Baliga’s figure of merit of 3444. In addition,
the large bandgap of <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>gives stability in harsh
environment operation at high temperatures. </p>
<p>Although low-cost
large-size <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>native bulk substrates
can be realized by melt growth methods, the unique property that (100) surface
of <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>has a large lattice constant of 12.23 Å allows it to be cleaved easily into thin and long
nano-membranes. Therefore, <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>FETs on foreign substrates
by transferring can be fabricated and investigated before <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>epitaxy technology becomes mature and economical viable. Moreover,
integrating <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>on high thermal
conductivity materials has an advantage in terms of suppressing self-heating effects.
</p><p>In this dissertation, structural and material
innovations to overcome and improve critical challenges are summarized as
follows: 1) Top-gate nano-membrane <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>FETs on a high thermal conductivity diamond
substrate with record high maximum drain current densities are demonstrated.
The reduced self-heating effect due to high thermal conductivity of the
substrate was verified by thermoreflectance measurement. 2) Local
electro-thermal effect by electrical bias was applied to enhance the electrical
performance of devices and improvements of electrical properties were shown
after the annealing. 3) Thin thermal bridge materials such as HfO<sub>2 </sub>and ZrO<sub>2 </sub>were inserted between <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>and
a sapphire substrate to reduce self heating effects without using a diamond
substrate. The improved thermal performance of the device was analyzed by
phonon density of states plots of <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>and the thin film materials. 4) Nano-membrane
tri-gate <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>FETs on SiO<sub>2</sub>/Si substrate fabricated via exfoliation have been demonstrated for the
first time. 5) Using the robustness of <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>in harsh environments, <i>β</i>-Ga<sub>2</sub>O<sub>3 </sub>ferroelectric
FETs operating as synaptic devices up to 400 °C were demonstrated. The result
offers the potential to use the novel device for ultra-wide bandgap logic
applications, specifically neuromorphic computing exposed to harsh
environments.<br></p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14167478 |
| Date | 12 March 2021 |
| Creators | Jinhyun Noh (10225202) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/STRUCTURAL_AND_MATERIAL_INNOVATIONS_FOR_HIGH_PERFORMANCE_BETA-GALLIUM_OXIDE_NANO-MEMBRANE_FETS/14167478 |
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