A Series-Shunt Compact GaN HEMT With High Isolation and Broadband Performance for RF Switch Application

This article first proposes a series-shunt compact (SSC) radio frequency (RF) switch design based on gallium nitride (GaN) high-electron-mobility transistors (HEMTs) which can significantly improve the device’s isolation (ISO) and mitigate the degradation of insertion loss (IL). The design follows a distributed architecture, introducing a shunt structure on conventional HEMTs and tightly coupling the capacitances of the series and shunt parts’ active regions. This leads to an increase in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$C_{\mathbf {on}}$ </tex-math></inline-formula> during the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small>-state, while the depletion of the negatively biased shunt gate enhances signal shielding, avoiding the effect of increased frequency on IL degradation. Moreover, the device exhibits excellent ISO performance in the <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small>-state. Overall, these design characteristics enable the 500 nm gate-length SSC GaN HEMT to achieve an ISO larger than 14 dB, an IL flatness of 0.38 dB across the 2–20 GHz range, and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R_{\mathbf {on}} C_{\mathbf {off}}$ </tex-math></inline-formula> coefficient of 478 fs. Currently, the SSC HEMT boasts state-of-the-art ISO metrics in single-cell devices, outperforming even some typical circuit topologies. Additionally, the SSC HEMT achieves a maximum output power (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P_{\mathbf {max}}$ </tex-math></inline-formula>) >37 dBm and an output third-order intercept point (OIP3) = 66 dBm at 3.6 GHz. These results demonstrate the great potential of the SSC HEMT in improving ISO and mitigating IL degradation across a broad frequency band, providing new possibilities for device selection in broadband RF circuits.