6-16am-poster-2 nanoelectronics research center ... session...6-16am-poster-2 peak intensity (cps)...

Reference

TBTDEN

1. Background

Development of NbN films by atomic layer deposition for Superconducting Tunnel Junction particle detectors with a high

operating temperatureM. Ukibe, and Go Fujii

National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, Ibaraki, 305-8568, JAPAN

Nanoelectronics Research Center

A) Understanding the evolution of molecules in spaceneed to evaluate quantitatively dissociationbranching ratios and the yields of neutral products indissociative electron-ion recombination (DR)processes.

The combination of a solid-state kinetic-energy-sensitive superconductingtunnel junction (STJ) particle detector and tandem mass spectrometers (MS) ora compact electrostatic storage rings.[2][3]

[2] M. Ohkubo, et al., IJMS 299, 94 (2011), doi: 10.1016/j.ijms.2010.09.027

B) The powerful analytical instrument of the DR processes

fabricated at AISTMS/KEMS instrument, AIST, Tsukuba

Lab-based MS/MS

[3] T. Tanabe, et. al., Dissociative Recombination of Molecular Ions with Electrons, p.p. 75-85(2003)

[1] Scott Sandford, et. al., The Astronomy and Astrophysics Decadal Survey, Science White Papers,257(2009)

[1]

Solid state kinetic-energy-sensitive

Nb/Al STJ detector Electrostatic Storage Ring

or

MS instruments

+

2. Difficulties of the STJ operation in MSA) An appropriate operation temperature of Nb/Al STJs : 0.3 K

IR shield

Particles can pass through holes in IR shield

B) Large thermal inflows from room temperature to STJs for a high throughputA large number of wirings (>100) for obtaining a large detection areaInsufficient thermal filter setup for the particles sources

It is necessary for particles to pass IR shieldsC) STJ detectors with high operation temperature > 1 K

Operation temperature < Transition temperature (TC ) / 10NbN (TC : 17.8 K for 100 nm[4] ) is appropriate

[4] A. Shoji, IEEE Tran. Mag. 27, p.p. 3184(1991)

D) NbN/AlN/NbN STJ (NbN-STJ)Nice lattice matching : NbN(0.439 nm (a-axis)) and AlN (0.498 nm (c-axis))

Full nitride multilayerAlN thickness should be controlled between 1.4 and 1.6 nm in order to realize a JC value between 100 and 1000 A/cm2[5]

[5] Z. Wang, et. Al., Appl. Phys. Lett., 75, p.p. 701(1999)

Full epitaxial multilayerGood tunnel barrier

E) Atomic layer deposition (ALD) is best for the deposition of NbN-STJsNbN films deposited by an ALD tended to exhibit a low TC of about 10 K [6].

3. Experiments

[6] Mario Ziegler et.al., Supercond. Sci. Technol. 26, 025008 (2013)

• Source (precursors) of NbN : TBTDEN [C16H39N4Nb]• Substrate : M-plain sapphire wafer• ALD : Ultratech Fiji 200 G2 • Substrate temperature(Tsub) : 570 K• Film thickness (tNbN) : 50 nm• Dissociation of TBTDEN : N2 plasma

[7] http://www.longsun.asia/uploadfile/upload/2015072113420828.pdf

Ultratech Fiji 200 G2 [7]

A) Deposition condition

We have tried improving the superconducting properties of ALD NbNfilms by a post-deposition RTP to realize a high TC about 17 K.

B) Anneal condition• Annealer : ANNEALSYS AS-One 100• Process gas : N2 at of 1 atm• Anneal temperature : 770, 870, 970, 1050, 1120 K• Temperature ramp rate : 50 K/sec • Anneal time : 20 ~ 2000 sec

AS-One 100

C) Evaluation of film characteristics(i) X-ray diffraction • Diffractometer :Rigaku Ultima X Multipurpose X-ray diffraction system• Measurement : Grazing incident(0.6 degree), θ-2θ, In-plane, φ-scan, Pole figure (ii) Surface morphology• SPM : Shimadzu SFT-4500 scanning probe microscope• Scan area : 500 x 500 nm(iii) R-T curve• Pattern size : A line patter of 50 µm width and 1 mm long• Cryostat : 4K GM

4. Results

X-ray diffraction pattern(GI) of a NbN film annealedat 870 K, 200 sec.

A) Crystal structure• ALD NbN film on M-plain sapphire wafer : 110 orientation• After the anneal process at 970 K, a part of the cubic NbN transformed into

tetragonal NbN.• Crystallite size : ALD film(9-11 nm) < Sputter film (14-16 nm)• Best crystallinity so far at 870 K, 200 sec

Pole figure of a NbN film annealed at 770 K, 2000 sec. Itshows that the NbN film has 110 orientation.

B) Surface morphology• The surface of the NbN film became rough by the anneal.• With increasing the anneal temperature, the root mean square roughness (Sq)

was considerably enlarged but wasn’t larger than that of the sputter film.• The grain size of the NbN in the ALD film increased by the anneal too.

C) R-T curves• The TC of the ALD NbN film was 12.35 K,

higher than that of the previous data [6]and was increased to 13.37K by theanneal of 770K, 2000 sec.

• The RRR values of the ALD NbN filmswere smaller than that of the sputter film.

5. Conclusion• We succeeded in depositing a 50 nm - thick NbN film on M-plain sapphire with

relatively high TC of 12.35 K.• The anneal certainly changed the crystal structure conditions of the ALD NbN

films and the TC was improved up to 13.37 K.• It is considered that the enlargement of the grain size of the NbN by the anneal

process was occurred by an agglutination of many NbN crystallites, not by thecrystal growth of each NbN crystallite.

• It is necessary to perform the further investigation in order to decide theoptimal anneal condition of the ALD NbN films.

This work was supported by JSPS KAKENHI Grant Number 15H03599. A part of this work was conducted at the AIST Nano-Processing Facility.

AcknowledgmentThe authors thank H. Yamamori and S. Shiki for their help with the experiments, and the clean room members of analog-digital superconductivity (CRAVITY) forperforming experiments.

6-16am-Poster-2

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Development of NbN films by atomic layer deposition for Superconducting Tunnel Junction particle detectors with a high operating temperature�M. Ukibe, and Go Fujii�National Institute of Advanced Industrial Science and Technology, 1-1-1, Umezono, Tsukuba, Ibaraki, 305-8568, JAPAN