Presentation Information
[EDP2-09]Effect of film thickness on the gain of kinetic-inductance traveling-wave parametric amplifier at millimeter wavelength
*Hayato Kondo1, Masanori Takeda1 (1. Shizuoka Univ. (Japan))
Keywords:
parametric amplifier,kinetic inductance,millimeter wave
Kinetic-inductance traveling-wave parametric amplifiers (KITWPAs) have demonstrated broadband gain, noise performance approaching the quantum limit, and extremely low power dissipation in the microwave regime. Previous work has pursued high gain by using high-resistivity thin films to enhance the kinetic-inductance nonlinearity. However, the high-frequency surface resistance increases with both temperature and frequency, which raises transmission loss. In the millimeter-wave band at 4 K, this loss can become significant, so using high-resistivity films may in fact reduce the achievable gain. In this study, we investigate whether increasing the thickness of NbTiN films enables high-gain operation in the millimeter-wave regime.
We modeled a KITWPA using an NbTiN microstrip with an amorphous-silicon dielectric and targeted a band center at 45 GHz. The dielectric and ground-plane thicknesses are both 200 nm, and the conductor thickness t is set to 20, 50, and 100 nm. Gain is evaluated using coupled-mode equations that include transmission loss.
At 4 K and millimeter-wave frequency, thicker films exhibit lower transmission loss, enabling higher signal amplification with increasing line length. Moreover, when the line length for each film thickness is set to maximize gain, the t = 100 nm device provides the widest bandwidth over which the gain exceeds 20 dB.
These results indicate that, for millimeter-wave KITWPAs operating at 4 K, reducing transmission loss is more critical for achieving high gain than further increasing nonlinearity, and that increasing NbTiN film thickness is an effective approach to high-gain, broadband performance.
We modeled a KITWPA using an NbTiN microstrip with an amorphous-silicon dielectric and targeted a band center at 45 GHz. The dielectric and ground-plane thicknesses are both 200 nm, and the conductor thickness t is set to 20, 50, and 100 nm. Gain is evaluated using coupled-mode equations that include transmission loss.
At 4 K and millimeter-wave frequency, thicker films exhibit lower transmission loss, enabling higher signal amplification with increasing line length. Moreover, when the line length for each film thickness is set to maximize gain, the t = 100 nm device provides the widest bandwidth over which the gain exceeds 20 dB.
These results indicate that, for millimeter-wave KITWPAs operating at 4 K, reducing transmission loss is more critical for achieving high gain than further increasing nonlinearity, and that increasing NbTiN film thickness is an effective approach to high-gain, broadband performance.