Hybrid MKIDs with ground-side deposition- A novel method for microwave detection with a resonator separated from antenna

H. Watanabe, M. Hazumia, H. Ishinob, A. Kibayashib, Y. Kibeb, S. Mimac, S. Oguria, C. Otanic, N. Satoa, O. Tajimaa, K. Takahashic, and M. Yoshidaa

SOKENDAI, Tsukuba, Ibaraki, 305-0801, Japana High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, 305-0801, Japan

b Okayama University, Okayama, 700-8530, Japanc Terahertz-wave Research Group, RIKEN, 2-1 Hirosawa, Wako, Saitama, 351-0198, Japan

Light satellite for the studies of B-mode polarization and Inflation from cosmic background Radiation Detection

1． LiteBIRD

Quality factor as a function of physical temperature of Al-Nb hybrid MKIDs with ground-side deposition

Microwave Kinetic Inductance Detectors (MKIDs) as a good candidate

- High Q-value of resonance results in good NEP.

- Many signals from detectors can be multiplexed.

- No bias is required.

Requirements for detectors

MKIDs are superconducting cooper-pair breaking detectors.It’s very simple. It consists of three components: feed line, resonator, and antenna.

Principle of signal detection1. Reference RF (~5GHz) is fed into the feed line, which is coupled to resonators. Each resonator has

individual resonance frequency, which is determined by inductance of the resonator, i.e. length of the resonator. The output microwave from the feed line has resonant peaks.

2. Millimeter waves (signals) that are picked up by the antenna break cooper-pairs in the resonator. It results in the variation of kinetic inductance (Mattis-Bardeen : anomalous skin effect).

3. The variation of the inductance induces change of the resonance frequency as well as change of the resonance phase.

2. MKIDs

Frequency of RF (GHz)

Resonance withoutany signal input

Variation of kinetic inductance induces the shifts of resonance peaks.

Millimeter waves above twice of gap energy, i.e. hν>2Δ, break cooper-pairs. As a result, the kinetic inductance changes.

MKIDs

Sorption refrigerator with pulse tube cooler

Coaxial cable

Equivalent diagram of LC-resonator circuit

4 ． Performance evaluations in the laboratory

Inflation potential: V1/4 ~ 1016 x (r/0.01)1/4 GeV (with slow-roll approximation) “r” is Tensor-to-Scalar ratio (T/S), which is proportional to the B-modes intensity. Many models predict r = 0.01 ~ 0.10.

< 3 mKarcmin with 2 years of full-sky observation

~2,000 pixels x 10-18 (WHz-1/2) NEP detectors

Sensitive for multi-frequency bands for foreground removal

four or more frequency bands in 50-270 GHz

LiteBIRD is a small satellite for observation of the CMB B-mode polarization. The B-mode is a smoking-gun signature of inflationary universe. Generic prediction of the inflation models is generation of primordial gravitational waves, which results in the B-modes. Since the B-mode power is proportional to the intensity of the primordial gravitational waves, i.e. potential energy of the inflation, precise measurements of the CMB polarization could determine the energy scale of inflation.

We evaluate the performance of developed MKIDs under the 0.3 Kelvin condition.

We measured the quality factor by changing the physical temperature of MKIDs device;- Best Q~1,000,000 at 0.33K.

Next step• Measure the sensitivity and

noise.• Produce more MKIDs and

evaluate a fraction of good channels.

5 ． SummaryWe have been developing MKIDs for LiteBIRD.

We propose hybrid MKIDs with ground-side deposition.

• Advantages- Radiation loss due to leakage from the resonator to the antenna can be avoided.- This design can also adopt the easier millimeter wave filter design.- It’s simple design allows us to use a contact aligner for fabrication.

• Test results- Quality factors increase as temperature decreases.- Best Q ~ 1,000,000 at 0.33K.

Poster P-19

Resonance with signal

Cooper-pair

Signals from antenna

Material TC (Kelvin) Frequency corresponding to 2D (GHz)

Niobium (Nb) 9.2 750

Aluminum (Al) 1.2 80

MicrowaveResonator

Dipole Antenna

Feed Line

100μm

～5GHz

Feed Line

CMB signal(~100GHz)

RF IN

RF OUT

λ/2 MKIDs

RF OUT

RF IN

3. Ground-side deposition

Hybrid MKIDsHaving a localized absorption area for deposition of input power from an antenna, which is often called “hybrid technique”, is a popular way to improve a sensitivity of the detector. Hybrid MKIDs are made using two different superconducting materials. Our hybrid MKIDs are fabricated using Al and Nb.

0.3K stage

左か

ら

NbSi Si

AlNbNbSiO2

SiNb AlNb

SiO2

Antenna

Cross-section view

Our proposal is to have an absorption area that is located on the ground-side of the coplanar waveguide (CPW). A microstrip line (MSL) connects the absorption area and the antenna.

300 350 400 450 500 550 600 650 700 750 8000

200000

400000

600000

800000

1000000

1200000

No.1No.2No.3No.4No.5

Temperature （ｍＫ）

Qu

alit

y fa

ctor

Ground

Advantages- Radiation loss due to leakage from the resonator to the antenna can be avoided.

- Antenna and resonator are not connected directly.- This design can also adopt the easier millimeter wave filter design.- It’s simple design allows us to use a contact aligner for fabrication.

Hence radiation with 750 GHz> f >80 GHz traveling from the antenna into resonator will be absorbed only in the Al. The quasiparticles created by signals are confined within the Al due to the difference in superconducting gap between two materials.

NbResist

Al

Etching

Al

① ②

④③

⑤Lift off

Nb

No2

Quasiparticles