研究目的
Investigating titanium nitride (TiN) thin films deposited via atomic layer deposition (ALD) for microwave kinetic inductance detectors (MKID) to develop arrays for passive terahertz imaging applications.
研究成果
Prototype TiN MKID subarray demonstrated NEPopt ≈ 2.3 × 10?15 W/√Hz and time constant τ ≈ 31 μs at 297 pW optical load, meeting requirements for passive THz imaging but not yet source-noise-limited. Further optimization of pixel design, read-out noise, and ALD process is needed to achieve better performance and enable operation at higher temperatures.
研究不足
The detector NEP is higher than the photon noise of the source, indicating non-optimized performance. Read-out noise at frequencies below 1 kHz and optical efficiency need improvement. The study uses non-optimized pixel designs and initial ALD films, with potential for further optimization in growth process and device geometry.
1：Experimental Design and Method Selection:
The study involved depositing TiN thin films using an in-house ALD process with TDMAT and H2/N2 plasma precursors, followed by characterization of superconducting properties and fabrication of MKID test resonator structures. The design rationale was to optimize TiN films for high-resistivity and adjustable Tc for use in MKIDs operating at higher temperatures than Al-based detectors.
2：Sample Selection and Data Sources:
High-resistivity Si (111) substrates were used, treated with buffered HF. Films of thicknesses 15, 30, and 60 nm were deposited. Data were collected from measurements of film properties and resonator performance.
3：List of Experimental Equipment and Materials:
ALD system (Oxford Instruments FlexAL), transmission electron microscope (TEM) for imaging, photolithography equipment for patterning, dry etcher with Cl2/Ar plasma, 3He cryostat for low-temperature measurements, vector network analyzer (VNA), homodyne read-out system, cold low noise amplifier, blackbody source with filter stack, HFSS software for simulations.
4：Experimental Procedures and Operational Workflow:
Substrates were prepared with HF dip, heated to 350°C, and films deposited via ALD cycles. Films were characterized for thickness, resistivity, Rs, and Tc. MKID devices were fabricated using photolithography and dry etching. Devices were tested in a cryostat at 300 mK, with microwave transmission measured using VNA and homodyne read-out, and optical performance assessed with a blackbody source.
5：Data Analysis Methods:
Resonance parameters were extracted by fitting S21 data. Optical responsivity and noise equivalent power (NEP) were calculated from frequency shifts and power spectral density measurements. Simulations were performed using HFSS for optical efficiency.
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ALD system
FlexAL
Oxford Instruments
Deposition of titanium nitride thin films via atomic layer deposition
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Transmission electron microscope
Imaging cross-sections of TiN films to analyze microstructure
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Vector network analyzer
Measuring microwave transmission S21 of resonator structures
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Homodyne read-out system
Measuring I and Q signals for frequency perturbation extraction
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Cold low noise amplifier
Amplifying microwave signals in cryogenic setup
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3He cryostat
Providing low-temperature environment for device testing
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Blackbody source
Providing optical illumination for detector testing
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HFSS software
Simulating optical efficiency and absorption of EM radiation in MKID devices
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