Sung-Gi Hur

Characterization of photoconductive CdS thin films prepared on glass substrates for photoconductive-sensor applications

Cadmium sulfide (CdS) thin films with n-type semiconductor characteristics were prepared at room temperature on glass substrates by radio-frequency magnetron sputtering for photoconductive-sensor applications. Films deposited at room temperature exhibit polycrystalline phases and show smooth surface morphologies. The deposition rate of the films decreases with increasing working pressure. The dark- and photoresistances in 400-nm-thick CdS films deposited at 6.7×10−1Pa and 80W were approximately 1×105 and 3×104Ω∕sq, respectively. Lowering both the dark- and photoresistances lowers the sensitivity (Rdark∕Rphoto) of the resistance.

Effect of the deposition temperature on temperature coefficient of resistance in CuNi thin film resistors

A constantan composition of Cu54Ni46 showing an near zero TCR value was obtained using a Ni power of 100W and a Cu power of 50W by dc magnetron cosputtering. The grain size increases and resistivity of the films decreases with increasing deposition temperature. The crystallinity of the films definitely influences the TCR value, which is an important parameter in resistor devices. The films deposited at 100°C exhibited a near zero TCR value of approximately 5ppm∕°C and the positive TCR values increased with increasing deposition temperature. The films deposited above 100°C do not exhibit irreversibility of the resistance with increasing deposition temperature.

Metalorganic chemical vapor deposition of non-GST chalcogenide materials for phase change memory applications

The feasibility of InSbTe (IST) chalcogenide new materials by metalorganic chemical vapor deposition (MOCVD) was demonstrated for PRAM applications. IST-MOCVD at a low temperature of 250 °C resulted in a favorable conformal deposition in the trench structure with a high aspect ratio. The IST films grown at 250 °C showed the highest resistance of approximately 108 Ω/sq, suggesting the amorphous phase of IST and the films grown at 300 °C include various crystalline phases of IST, In–Sb, and In–Te. MOCVD-IST films exhibited a step-coverage of about 95% in the trench structure with a 5 : 1 aspect ratio (a height of 500 nm and a diameter of 100 nm) and also showed reliable filling of the trench under appropriate deposition conditions. Phase switching between amorphous and crystalline states in the IST films grown on a trench structure at a high-aspect ratio (3.5 : 1) was demonstrated showing functional characteristics for applications in memory devices. The IST-based chalcogenide films used included various crystallized phases of In–Sb–Te, In–Sb and In–Te, which proved to be favorable for multilevel data storage.

Enhancement of Photosensitivity in CdS Thin Films Incorporated by Hydrogen

CdS films, 200 nm thick, for photoconductive sensor applications were prepared at various H 2 /(Ar + H 2 ) flow ratios on glass substrates at room temperature by radio-frequency magnetron sputtering. The sulfur concentration in CdS films crystallized at room temperature with (002) preferred orientation depends directly on the hydrogen atmosphere; the surface roughness of the films gradually increases with increasing hydrogen atmosphere. Films deposited at 8% of H 2 /(Ar + H 2 ) exhibit an abrupt decrease of dark- and photoresistance, showing a low photosensitivity (R dark /R photo ). Films deposited at a hydrogen atmosphere of 42% exhibit a photosensitivity of 5 X 10 3 , maintaining a photoresistance of an approximately 2 X 10 4 Ω/□. The dark- and photoresistance values of CdS films were related by a composition, surface roughness, and defect sites within the bandgap.

High-Resistivity Thin-Film Resistors Grown Using

Thin-film resistors for the high resistivity and the low temperature coefficient of resistance (TCR) applications were prepared using the CrB2-Si-SiC (it was abbreviated as CrSS) target in an argon and oxygen mixture ambient on the SiO2/Si substrates by radio-frequency magnetron sputtering. The microstructural and electrical properties of the films were investigated for various deposition temperatures. The resistivity and the TCR values of the films were remarkably varied with increasing deposition temperature. Abrupt variations in the resistivity and the TCR values in the films grown above 550°C were attributed to the nanocrystalline Cr2SiO4 phases embedded in the amorphous phases. The 91-nm-thick samples grown at 565°C in an argon and oxygen mixture ambient exhibited a resistivity as high as 1.0 kΩ/sq and a TCR value as low as -6 ppm/°C. The resistivity and the near-zero TCR values of the thin films grown at various temperatures are a strong candidate for high-resistivity thin-film resistor applications.

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A constantan composition of Cu 5 4 Ni 4 6 showing a near-zero temperature coefficient of resistance (TCR) value was obtained on AlN substrates using a Ni power of 100 W and a Cu power of 50 W by dc magnetron cosputtering. The grain size increases and resistivity of the films decreases with increasing deposition temperature. The crystallinity of the films definitely influences the TCR value, which is an important parameter in resistor devices. The films deposited at 100°C exhibited a near-zero TCR value of approximately 7 ppm/°C and the positive TCR values increased with increasing deposition temperature. The films deposited above 100°C do not exhibit irreversibility of the resistance with increasing deposition temperature.

–Si–SiC Materials by Radio-Frequency Magnetron Sputtering

NiCr alloys prepared by dc magnetron sputtering are considered to apply simultaneously both the absorption layer and the top electrode on PZT thin films for infrared sensors. NiCr alloys deposited with dc powers of Ni 80 and Cr 50 W showed the most stable oxidation resistance even at 600°C in an oxygen ambient. They have a resistivity of approximately 70 μΩ-cm and a rms roughness of 2.0 nm in samples annealed at 600°C for 5 min in O2. The NiCr/PZT/Pt capacitors showed a well-saturated hysteresis loop having a remanent polarization of 20 μC/cm2. Ultra-thin NiCr alloys showed a possibility as a top electrode for infrared sensors.

The Structural and Electrical Properties of CuNi Thin-Film Resistors Grown on AlN Substrates for Π -Type Attenuator Application

Cadmium sulfide (CdS) thin film for flexible optical device applications were prepared at flow ratios on polyethersulfon (PES) flexible polymer substrates at room temperature by radio frequency magnetron sputtering technique. The CdS thin films deposited at room temperature showed a (002) preferred orientation and the smooth surface morphologies. Films deposited at a hydrogen flow ratio of 25% exhibited a photo- and dark-sheet resistance of about 50 and , respectively. From the result of the bending test, CdS films exhibit a strong adhesion with the PES polymer substrates and the passivation layer deposited on the CdS films only shows an increase of the resistance of 8.4% after exposure for 120 h in air atmosphere.

NiCr Alloy As Both Absorption Layer and Top Electrode onto Pb(Zr0.3Ti0.7)O3 Thin Films for Infrared Sensors

NiCr thin films were fabricated by rf magnetron sputtering for applying to both the top electrode and absorption layer on Pb(Zr, Ti)O(PZT) thin films for infrared sensors. The rms roughness and resistivity of NiCr films prepared with Ni power of 80 W and Cr power of 50 W showed the most stable oxidation resistance after annealing at for 5 min in oxygen ambient. The rms roughness and resistivity of NiCr films annealed at in oxygen ambient were about 2 and Ω-cm, respectively. As-deposited Ni/PZT/Pt and NiCr (Ni 80 W, Cr 50 W)/PZT/Pt structures showed well saturated hysteresis loops. However, in case of the samples annealed at in oxygen ambient, only NiCr/PZT/Pt showed saturated loops having a remanent polarization of C/. Ultra-thin NiCr films showed a possibility as a top electrode for infrared sensors.