MgB$_2$ Thermal Kinetic Inductance Detector

Abstract

Thermal Kinetic Inductance Detectors (TKIDs) inherently combine the phonon-limited noise performance of traditional bolometers with the array scalability and responsivity of superconducting kinetic inductance detectors. Using a superconducting resonator as the thermally sensitive element provides high responsivity and tunable dynamic range, with phonon noise set by the cryogenic operating temperature of the free-standing membrane. In this work, MgB$_2$-based TKIDs are demonstrated operating from below 1 K up to 20 K with characterized noise-equivalent power (NEP) using integrated on-membrane heaters. A comprehensive characterization of electrical, thermal, and noise properties is presented. Phonon noise-limited performance is demonstrated from 4 to 8 K.

Figures (6)

• Figure 1: MgB$_2$ TKID design, (a) schematic diagram of the TKID, and (b) SEM of a released TKID membrane.
• Figure 2: Measured and fitted quality factors of an MgB$_2$ TKID resonator at different temperatures. Inset shows the $S_{21}$ magnitude vs frequency over the same temperature range for the device.
• Figure 3: TKID performance as a function of heater power $P_H$ from 250 mK to 20 K. TKID $S_{21}$ sweeps with different DC heater powers applied at a bath temperature of (a) 4.5 K and (b) 10 K. These measurements are used to calculate $G$ for a specific bath temperature. (c) Measured thermal conductance of the TKID. The heater resistance for the TKID at JPL is normalized to match the thermal conductance of the device measured at ASU. Both measurements exhibit nearly identical temperature dependence.
• Figure 4: Thermal response as a function of membrane temperature, (a) TKID response vs. membrane temperature at a fixed bath temperature under different DC heater powers, and (b) response rolloff frequency (left axis) and time constant (right axis) measured at fixed bath temperatures from 250 mK to 17.9K.
• Figure 5: NEP spectrum of the TKID noise at 4.56 K. The in-phase (I) and quadrature (Q) components of the noise signal are detector and readout noise, respectively.