# 18th International Workshop on Low Temperature Detectors (LTD-18)

22-26 July 2019
Milano
Europe/Rome timezone

## Optimized design for on chip Fabry-Pérot resonators

25 Jul 2019, 17:45
1h 15m
Piazza Città di Lombardia (Milano)

### Piazza Città di Lombardia

#### Milano

Piazza Città di Lombardia, 1, 20124 Milano MI
Poster Low Temperature Detector fabrication techniques and materials

### Speaker

Kevin Kouwenhoven (Delft University of Technology)

### Description

On-chip spectrometers, such as DESHIMA and SuperSpec, require transmission lines with $Q_i>10^4$ to achieve sufficient system efficiency. Transmission lines with lower $Q_i$ would introduce too much losses in the line from antenna to filter and in the filters themselves. Data regarding the losses of transmission lines at THz frequencies and sub-K temperatures is severely lacking. An on-chip Fabry-Pérot resonator can be used to measure the internal losses, $Q_i$, of a transmission line with high sensitivity at high frequencies. To create the in-line Fabry-Pérot resonator, a transmission line of certain length is coupled to an THz source via a twin-slot lens antenna on one side and to an Al-NbTiN hybrid MKID on the other side.

We show the detailed design of the Fabry-Pérot resonator to measure the losses of a dielectric in the order of $10^3 < Q_i < 10^5$. There are several experimental challenges for measuring $Q_i$. The first challenge is the limited frequency resolution of the source, due to which resolving high $Q$ can become impossible. Secondly we experimentally found that there is stray light coupled to the detector which causes a spurious response with a level of $-30dB$ with respect to the peak transmission of the Fabry-Pérot resonator. Taking these experimental challenges into account we design an on-chip Fabry-Pérot resonator for measurements of high $Q_i$ dielectrics. In this design we optimize the length, the mode number and the couplers of the resonator. Furthermore we use multiple resonators on a single chip, each coupled to a separate antenna and detector, with different $Q_c$ values. This design method is applicable for different dielectric materials and different transmission line configurations. Using this method we designed and fabricated a chip with which we measured a $Q_i\approx 10^4$ @ 350 GHz for a PECVD deposited a-Si dielectric.

Less than 5 years of experience since completion of Ph.D N Y

### Primary authors

Kevin Kouwenhoven (Delft University of Technology) Sebastian Hähnle (SRON, Netherlands Institute for Space Research) David Thoen (Delft University of Technology) Mr Vignesh Murugesan (SRON, Netherlands Institute for Space Research) Prof. Jochem Baselmans (SRON)

### Presentation Materials

 pitch_k_kouwenhoven_16_9.pdf poster_k_kouwenhoven.pdf