R&D of quantum photo-sensor
based on superconductor withcryo-SOI readout
INAUGURAL SYMPOSIUM FOR THE TOMONAGA CNETER FOR THE HISTORY OF THE UNIVERSE

University of Tsukuba
Rena Wakasa

Motivation
 Neutrino’s mass is not zero.
➢ Heavier neutrino can decay into lighter neutrino.
➢ An energy of photon from neutrino decay is given
For neutrino oscillation experiments,
222𝑚 −𝑚Δ𝑚32= 2.44 ± 0.06 × 10−3 eV 2𝐸𝛾 = 3 2 .
22𝑚3Δ𝑚21= 7.52 ± 0.18 × 10−5 eV 2Can obtain neutrino mass to measure the energy.
➢ Assuming 𝑚1 ≪ 𝑚2 < 𝑚3 and 𝑚3 = 50 meV,the energy is expected𝐸𝛾 = 25 meV 𝜆=50μm .
 Neutrino’s lifetime is very long.
➢ 𝜏SM~1043 years➢ 𝜏LRSM~1017 years

𝛾𝑙L

𝜈2L
𝛾𝑙L

𝑊L𝑙L

＊
𝜈3R

Standard model

𝜈2L
𝑊1𝑙R
𝜈3R

Left-Rightsymmetric model

Search for neutrino decay using
Cosmic Background Neutrino (CνB, 𝜌~110 /cm3 )as the neutrino source.

2Surface brightness I [MJy/sr]

Signal of CνB Decay and Backgrounds
CMB

Zodiacal Emission

AKARI COBE Surface Brightness➢ Zodiacal Emission

𝐼𝜈 ~8 MJy/sr➢ Cosmic Infrared

Zodiacal LightHigh Energy
Cutoff (25meV)

Background𝐼𝜈 ~0.1~0.5 MJy/sr➢ CνB Decay

ISD
DGL

SL

wavelength [m]E [meV]𝜏 = 1014 years𝐼𝜈 ~25 kJyΤsr 𝜆 = 50 μm

By measuring the energy
spectrum continuously,
we can see the CνB decay
signal as a high energy
cutoff.

To identify the shape edge, we need detector which
has better than 2% resolution for 𝐸𝛾 = 25 meV 𝜆=50 μm . 3

COBAND ExperimentCOsmic BAckground Neutrino Decay search Rocket Experiment➢ 200sec data acquisition at 200km height➢ Using 50×8 array of Nb/Al-STJ pixels withdiffractive grating covering 𝜆 = 40~80 μm,
we count photons for each wavelengths.

Improvement the lower limit ofneutrino lifetime from O(1012)
years to O(1014) years.

DiffractiveGrating Satellite Experiment➢ 100days measurement at satellite

𝟖Nb/Al-STJ 𝟓𝟎DAQ➢ STJ detector using Hafnium (Hf-STJ) achieves 2% energy resolution

if fano factor < 0.3 for 𝐸𝛾 = 25 meV.

Aiming at a sensitivity to neutrino lifetime
for O(1017) years.

4

STJ Detector
Superconducting Tunnel Junction
 Structure➢ STJ is detector consist ofSuperconductor/Insulator/Superconductor.

 Working Principle➢ An incident photon excites cooperΩpairs into quasi-particles in thesuperconductor.
➢ By applying a bias voltage, theΩ𝚫

quasi-particle tunnel throughinsulator.
𝐼 Characteristic of I-V Curve➢ Josephson current can suppress bymagnetic field.
➢ Leak current is constant below 1/10 ofcritical temperature.

𝐸F𝐼c𝟐𝜟/𝒆𝑉

w/o lightw/ light5

Development of Nb/Al-STJ
 Performance of our Nb/Al-STJ
NbAl➢ The signal width <10μs~400nm
𝐀𝐥𝟐 𝐎𝟑➢ The number of quasi-particles
SiO2
generated by 25meV single photon is𝐸𝛾
Size:10μm×10μm ~ 200μm×200μm
𝑁𝑒 = 𝐺Al
~250.
1.7Δ
Nb
AlHf
➢ The resolution is𝛿𝑁𝑒 /𝑁𝑒 ~15.5%
Δ[meV] 1.550 0.172 0.021
𝐸𝛾 :energy of incident photon
Tc[K]
9.20
1.140.13
𝐺Al :trapping gain ~10
Back tunneling
effect to enhance
Δ:band gap ~0.57meVSTJ size
𝑰𝐥𝐞𝐚𝐤 @300mKquasi-particles(Nb:100nm,Al:70nm)
50μm✕50μm
224±29pAdensity
20μm✕20μm

39±13pA

10μm✕10μm

14±7pA Requirement in Rocket Experiment➢ Leak current < 100pA

Nb/Al-STJs can count far infrared single photons
and achieved the requirement for leak current.
6

SOI-STJ
R&D of Cryogenic Amplifier
Nb/Al-STJs have not detected far infrared single photon yet.
It is affected by the large noise from the refrigerator’s
readout line about 5m.

Amplify the STJ signal by cryogenic amplifier placed near STJ.
FD-SOI MOSFET Requirement for the cryogenic amplifier➢ Operation at cryogenic temperature (<3K)

WL～50nm➢ Fast response speed (width of signal <10μs)
BOX SiO2Substrate➢ Low power consumption

 FD-SOI(Fully Depleted–Silicon On Insulator) MOSFET➢ FD-SOI MOSFET has the nano-channel layer.
➢ Low power consumption➢ Suppress charge-up of the body

※JAXA/ISAS confirmed working of
MOSFET under FD-SOI process at 4K.
T. Wada et al., J. Low. Temp.
Phys. 167, (2012) 602

Using FD-SOI MOSFET, we have developed
the cryogenic amplifier (SOI-STJ).

7Amplifying STJ Signal by SOI-STJ4SOI-STJ4Amplification
Common source amplifying circuit
Replaced the resistance by M2Feedback
Given a suitable input offset voltage by M3.
BufferSource follower circuit
Reduce the output impedance by M4 and M5.

STJ SOI

Amp.IN [μV]

STJ Signal

T=350mKLaser: λ=465nm,f=20kHz

70
60
5018μV

40-100-80-40-40-20

020

4060

80

100 μsec

4.7F

Amp.OUT [μV]

Output from SOI-STJ41600
1200
800
4000-100-80-40-40-2002040

SOI-STJ41.2mVsucceeded inamplifying the8100 μsec STJ signal!
6080

Summery COBAND Experiment aims to measure neutrinomasses.
 We have developed the STJ photo detector andcryogenic amplifier using FD-SOI-MOSFET(SOI-STJ) for rocket experiment.
 Nb/Al-STJs have achieved the requirement inrocket experiment.
 SOI-STJ4 succeed in amplifying the STJ

signal for visible laser.
9

Backup10

ロケット実験

 データ収集 上空200km
 収集時間200sec

 50✕8の検出器を使用
 検出器としてNb/Al-STJを使用

 遠赤外光が入射したかを検出

 3Heソープション減圧冷凍機を使用 到達温度：0.4K

 ニュートリノの寿命の下限値を修正
 𝜏 > 1014 years
 有意度5𝜎11

バックトンネリング効果
 バックトンネリングの仕組み✓ Nb層に光が入射し、クーパー対が励起

Nb

Al

絶縁膜

AlNb

して準粒子を生成✓ 生成された準粒子内あるものはそのまま

トンネル✓ トンネルしなかった準粒子はAl層での準粒子の存在確率を高める✓ トンネルした準粒子がAl層のクーパー対の片割れとクーパー対を作る✓ その際に余った電子が準粒子としてAl層で励起

 Nb/Al-STJではG~1012

STJの電流-電圧カーブ
 光応答を見る際は 𝑉 < 2Δ/𝑒の範囲の変化が見られる

ような電流値に固定する✓ リーク電流がノイズとなる

B

B𝐼𝑅n

クーパー対によるジョセフソンカレント
は磁場により抑制

𝐼c

2Δ/𝑒

𝑉

リーク電流
光on/off (磁場あり)
13リーク電流への要求
リーク電流の温度依存性

 Nb/Al-STJで25meVの1光子を測定する✓ 生成電荷数：𝑁𝑠𝑖𝑔 = 𝐺Al ∗~250𝐸𝛾
1.7Δ✓ ノイズによる電荷数：𝑁𝑙𝑒𝑎𝑘 =✓ 𝑁𝑠𝑖𝑔 の揺らぎ：𝛿𝑁𝑠𝑖𝑔 = 𝐺Al= 10 ×

産総研 藤井氏による測定

25meV
1.7×0.6meV

𝑖𝑙𝑒𝑎𝑘 ×𝜏𝑒𝐹∗

𝐸𝛾

Nb/Al-STJ(50μm□)

1.7Δ

Fano因子：𝐹～0.2✓ 𝑁𝑙𝑒𝑎𝑘 の揺らぎ：𝛿𝑁𝑙𝑒𝑎𝑘 =𝑁𝑙𝑒𝑎𝑘

M.Ukibe et al., Jpn. J.Appl. Phys. 51,010115(2012)
M.Ohkubo et al., IEEE Trans. Appl. Super, 24,2400208(2014)✓ STJの応答速度：𝜏~1𝜇s

 信号が300Hzで入ってくると考えリークによるノイズを1/10,検出効率97.5%と要求
Nb/Al-STJsize

Leak current@300mK50μm✕50μm

224±29pA

20μm✕20μm

39±13pA

現在、20μm角のNb/Al-STJで𝑖𝑙𝑒𝑎𝑘 ~100pAを達成！ 10μm✕10μm

14±7pA✓ 4 𝑁𝑙𝑒𝑎𝑘 = 𝑁𝑠𝑖𝑔 − 2𝑁𝑙𝑒𝑎𝑘

2+ 𝛿𝑁𝑠𝑖𝑔

𝑖𝑙𝑒𝑎𝑘 ~250pA

214

Comparison between new and old SOIamplifiers
SOI-STJ4
SOI-STJ5Circuit Common source circuit Charge integrating operational Input impedance Low input impedance caused by

𝑅in ~20kΩ

negative feedback （ideally, 0Ω）

The signal charges
transferred to SOI amplifieris ~1/6 of the total since
the STJ has capacitance of40pF
𝑉0 in parallel (@20μm sq.).
𝑅
𝐶𝑅in
𝐶STJ

STJ

amplifier with negative feedback

Almost all signal charges
are transferred to the SOI
𝑅FB
amplifier.
𝑉0𝑅
𝐶FB+𝐶STJ

STJ

15

帰還付き差動増幅回路による極低温電荷積分型増幅器の開発
SOI-STJ5
SOI-STJ4
 定電流モード
SOI増幅器はSTJ信号の電圧変化を読んで増幅する。

変更点

 定電圧モード
SOI増幅器はSTJ信号の電荷変換された電流変化を増幅する。

𝑅FB
𝑉0𝑉0𝑅

𝐶

𝑅𝐶

1mV →~1mV →

𝑅in
𝐶STJ

STJ

𝐶STJ

𝐶FB
+STJ

16

極低温におけるFD-SOI-MOSFETW FD-SOIL

Fully Depleted –Silicon On
Insulator～50nm

 省消費電力

N-ch MOSFETのIds-Vds特性Ids[uA]

Ids[uA] 浮遊帯効果の抑制

N-ch MOSFETのIds-Vgs特性

W/L=190/20
Vgs=2.0V

閾値電圧の移動
飽和電流値の増加

W/L=190/20
Vds=1.8V

Vgs[V]
Vds[V]
17
極低温において特性は変化するが、適切な動作点を使用すれば問題はない。

測定環境
He3 Sorption冷凍機(Oxford Instrument製)

読み出し配線光ファイバー
ヘルムホルツコイル

サンプル
中を見ると

He3減圧冷凍機 冷却能力一覧
各ステージには熱輻射を防ぐためにシールドがある

ステージ

最低到達温度[K]冷却能力60Kステージ

60

25W @65K

3Kステージ

2.8

0.7W @4.2K

最低温ステージ

0.3

100μW @350mK18