First Demonstration of Top T-Gate Beol-Compatible Indium-Oxide RF Transistors with Record Maximum Oscillation Frequency of 70 GHz

This work reports the first demonstration of back-end-of-line (BEOL)-compatible <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{In}_{2} \mathrm{O}_{3}$</tex> RF FETs on SiC substrate with a top T-gate architecture. The high thermal conductivity (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$k_{\mathrm{T}}$</tex>) SiC can alleviate self-heating effect (SHE) so that a high drain bias (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{V}_{\text{DS}}$</tex>) is applicable and the T-gate can help to reduce gate resistance (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{R}_{\mathrm{g}}$</tex>), both increases maximum oscillation frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(\mathrm{f}_{\text {max }}\right)$</tex>. Benefiting from a high top-gate field-effect mobility (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu_{\text{FE}}$</tex>) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$120 ~\text{cm}^{2} / \text{Vs}$</tex>, record <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\text {max }}$</tex> of 70 GHz and cut-off frequency (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\mathrm{T}}$</tex>) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\times$</tex> gate length (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{L}_{\mathrm{G}}$</tex>) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5.1 \text{GHz} \cdot \mu \mathrm{m}$</tex> are simultaneously achieved, where the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{\text {max }}$</tex> is more than 4 times of prior best reported value of BEOL-compatible oxide FETs. Combining with a high top-gate <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{I}_{\mathrm{D}, \max }=2.28 ~\mathrm{A} / \text{mm}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{g}_{\mathrm{m}, \max }\ =1.1 ~\mathrm{S} / \text{mm}$</tex>, as well as a low <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{SS}=80 \text{mV} / \text{dec}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{DIBL}=60\ \text{mV} / \mathrm{V}$</tex>, atomic-layer-deposited (ALD) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{In}_{2} \mathrm{O}_{3}$</tex> transistors show their great promise for BEOL-compatible RF applications.