First Demonstration of BEOL-Compatible Co-Sputter Deposited $\text{Te}_{1-x} \text{Se}_{x}$ p-FETs Enabling 3D Stackable Oxide Semiconductor CFET, DRAM, and First CFET-Structured SRAM

We report the world's first BEOL-compatible p-type Tellurium <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }_{0.8}$</tex> Selenium <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$_{0.2}\left(\text{Te}_{0.8} \text{Se}_{0.2}\right)$</tex> FETs with aggressively-scaled channel length (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$L_{\text{ch}}$</tex>) of 50 nm, achieved through Te-Se co-sputtering for bandgap tuning and performance improvement. Our <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Te}_{0.8} \text{Se}_{0.2}$</tex> FETs exhibit outstanding performance, including a mobility of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$24 \text{cm}^{2} / \mathrm{V} \cdot \mathrm{s}$</tex>, an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text {on }} / I_{\text {off }}$</tex> ratio <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$&gt;10^{4}$</tex>, and a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S S$</tex> of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\sim 300 \text{mV} /$</tex> Dec., all among the best. This device has enabled the realization of 3D stackable IGZO/ <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Te}_{0.8} \text{Se}_{0.2}$</tex> DRAM with excellent retention over 1000 s and short channel IGZO/Te <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${ }_{0.8} \text{Se}_{0.2}$</tex> CFET, achieving a gain of 38 at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$V_{\text{DD}}=2.5$</tex> V. Based on this CFET, we further experimentally demonstrated the world's first stacked oxide semiconductors CMOS SRAM with 4T footprint.