Kang-San Kim

Growth of polycrystalline 3C-SiC thin films for M/NEMS applications by CVD

This paper presents the growth conditions and characteristics of polycrystalline 3C-SiC (silicon carbide) thin films for M/NEMS applications related to harsh environments. The growth of the 3C-SiC thin film on the oxided Si wafers was carried out by APCVD using HMDS (hexamethyildisilane: precursor. Each samples were analyzed by XRD (X-ray diffraction), FT-IR (fourier transformation infrared spectroscopy), RHEED (reflection high energy electron diffraction), GDS (glow discharge spectrometer), XPS (X-ray photoelectron spectroscopy), SEM (scanning electron microscope) and TEM (tunneling electro microscope). Moreover, the electrical properties of the grown 3C-SiC thin film were evaluated by Hall effect. From these results, the grown 3C-SiC thin film is very good crystalline quality, surface like mirror and low defect. Therefore, the 3C-SiC thin film is suitable for extreme environment, Bio and RF M/NEMS applications in conjunction with Si fabrication technology.

Characteristics of polycrystalline 3C-SiC thin films grown on AlN buffer layer for M/NEMS applications

This paper describes the characteristics of poly (polycrystalline) 3C-SiC grown on and AlN substrates, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each substrate were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was . The surface chemical composition and the electron mobility of poly 3C-SiC grown on each substrate were investigated by XPS and Hall Effect, respectively. The chemical compositions of surface of poly 3C-SiC films grown on and AlN were not different. However, their electron mobilities were and , respectively. Therefore, since the electron mobility of poly 3C-SiC films grown on AlN buffer layer was two times higher than that of 3C-SiC/, a AlN film is a suitable material, as buffer layer, for the growth of poly 3C-SiC thin films with excellent properties for M/NEMS applications.

FABRICATION AND CHARACTERIZATION OF HYDROGEN SENSORS BASED ON TRANSFERRED GRAPHENE SYNTHESIZED BY ANNEALING OF Ni/3C-SiC THIN FILMS

This paper presents the formation of graphene and its application to hydrogen sensors. In this work, the graphene was synthesized by annealing process of 3C-SiC thin films with Ni transition layer. The Ni film was coated on a 3C-SiC layer grown thermal oxided Si substrates and used extracts of the substrates carbon atoms under rapid thermal annealing (RTA). Various parameters such as ramping speed, annealing time and cooling rate were evaluated for the optimized combination allowed for the reproducible synthesis of graphene using 3C-SiC thin films. Transfer process performed by Ni layer etching in HF solution and transferred graphene onto SiO2 shows the IG/ID ratio of 2.73. Resistivity hydrogen sensors were fabricated and evaluated with Pd and Pt nanoparticles in the room temperature with hydrogen range of 10–50 ppm. The response factor of devices with the Pd catalyst was 1.3 when exposed to 50 ppm hydrogen and it is able to detect as low as 10 ppm hydrogen at room temperature.

Synthesis of Graphene Using 3C-SiC Thin Films with Thermal Annealing Conditions

This paper describes the synthesis and characterization of graphene by RTA process. Amorphous 3C-SiC were deposited using APCVD for carbon source and Ni layer were employed for transition layer. Various parameters of the ramping speed, the annealing time and the cooling speed are evaluated for the optimized combination allowed for the reproducible fabrication of graphene using 3C-SiC thin film. For analysis of crystalline Raman spectra was employed. Transferred graphene shows a high IG/ID ratio of 2.73. SEM and TEM images show the optical transparency and 6 carbon network, respectively. Au electrode deposited on the transferred graphene shows linear I-V curve and its resistance is 358 Ω.

Fabrication of a Porous 3C-SiC Based Resistivity Hydrogen Sensor and Its Characteristics

Porous 3C-SiC(pSiC) samples with different pore diameters were prepared from poly crystalline N-type 3C-SiC by electrochemical anodization. The pSiC surface was chemically modified by the sputtering of Pd and Pt nano-particles as a hydrogen catalyst. Changes in resistance were monitored with hydrogen concentrations in the range of 110 ppm - 410 ppm. The variations of the electrical resistance in the presence of hydrogen demonstrated that Pd and Pt-deposited pSiC samples have the ability to detect hydrogen at room temperature. Regardless of the catalyst, the 25 nm pore diameter samples showed good response and recovery properties. However, the 60 nm samples showed unstable and slow response. It was found that the pore size affects the catalyst reaction and consequently, results in changes of the sensitivity to hydrogen.

Formation of porous 3C-SiC thin film by anodization with UV-LED

This paper describes the formation of porous 3C-SiC by anodization. 3C-SiC thin films were deposited on p-type Si(100) substrates by APCVD using HMDS(Hexamethyildisilane: ). UV-LED(380 nm) was used as a light source. The surface morphology was observed by SEM and the pore size was increased with increase of current density. Pore diameter of 70 90 nm was achieved at 7.1 mA/cm current density and 90 sec anodization time. FT-IR was conducted for chemical bonding of thin film and porous 3C-SiC. The Si-H bonding was observed in porous 3C-SiC around wavenumber 2100 cm. PL shows the band gap enegry of thin film(2.5 eV) and porous 3C-SiC(2.7 eV).

Mechanical properties of polycrystalline 3C-SiC thin films with various doping concentrations

This paper describes the mechanical properties of poly(polycrystalline) 3C-SiC thin films with various doping concentration, in which poly 3C-SiC thin fil`s mechanical properties according to the n-doping concentration 1(), 3(), and 5%() respectively were measured by nano indentation. In the case of -doping concentration, Young`s modulus and hardness were obtained as 270 and 30 GPa, respectively. When the surface roughness according to n-doping concentrations was investigated by AFM(atomic force microscope), the roughness of poly 3C-SiC thin films doped by 5% concentration was 15 nm, which is also the best of them.

Fabrication of CO 2 Gas Sensors Using Graphene Decorated Au Nanoparticles and Their Characteristics

Abstract This paper describes the fabrication and characterization of graphene based carbon dioxide (CO 2 ) gas sensors. Graphene wassynthesized by thermal decomposition of SiC. The resistivity CO 2 gas sensors were fabricated by pure graphene and graphene decoratedAu nanoparticles (NPs). The Au NPs with size of 10 nm were decorated on graphene. Au electrode deposited on the graphene showedOhmic contact and the sensors resistance changed following to various CO 2 concentrations. Resulting in resistance sensor using puregraphene can detect minimum of 100 ppm CO 2 concentration at 50 o C, whereas Au/graphene can detect minimum 2 ppm CO 2 concentration at same at 50 o C. Moreover, Au NPs catalyst improved the sensitivity of the graphene based CO 2 sensors. The responses ofpure graphene and Au/graphene are 0.04% and 0.24%, respectively, at 50 o C with 500 ppm CO 2 concentration. The optimum workingtemperature of CO 2 sensors is at 75 o C.Keywords : Carbon dioxide, Gas sensors, Graphene, Au nanoparticle

8.5.4 Fabrication and Characterization of MEMS Based Optical Hydrogen Sensors

This paper presents the fabrication and characterization of MEMS based optical type hydrogen sensors using transparent 3C-SiC membrane and photovoltaic effect. 3C-SiC membrane was fabricated by anisotropic etching. Gasochromic material of Pd was deposited by sputter on the 3C-SiC membrane for gas sensing layer. Pd and WO3 changes to transparency by exposure to hydrogen and the variations of light intensity generate the photovoltaic of P-N junction between N-type 3C-SiC and P-type Si. Photovoltaic increased with increase of hydrogen concentration. Pd/WO3 shows almost 2 times faster response and recovery toward hydrogen compared with Pd. However, low response factor is shown at Pd/WO3 by low penetration ratio.

Fabrication of Hydrogen Sensors Using Graphenes Decorated Nanoparticles and Their Characteristics

This paper presents the fabrication and characterization of graphene based hydrogen sensors. Graphene was synthesized by annealing process of Ni/3C-SiC thin films. Graphene was transferred onto oxidized Si substrates for fabrication of chemiresistive type hydrogen sensors. Au electrode on the graphene shows ohmic contact and the resistance is changed with hydrogen concentration. Nanoparticle catalysts of Pd and Pt were decorated. Response factor and response (recovery) time of hydrogen sensors based on the graphene are improved with catalysts. The response factors of pure graphene, Pt and Pd doped graphenes are 0.28, 0.6 and 1.26, respectively, at 50 ppm hydrogen concentration.