Surface acoustic wave characteristics of ZnO films grown on a polycrystalline 3C-SiC buffer layer

Zinc oxide (ZnO) thin films were deposited onto a polycrystalline (poly) 3C-SiC buffer layer for surface acoustic wave (SAW) applications using a magnetron sputtering system. Atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the ZnO grown on 3C-SiC/Si had a smooth surface, a dominant c-axis orientation and a lower residual stress in ZnO thin film compared to that grown directly onto Si substrate. In order to evaluate the SAW characteristics of ZnO films on a 3C-SiC buffer layer, the two-port SAW resonators, based on inter-digital transducer (IDT)/ZnO/3C-SiC/Si and IDT/ZnO/Si structures, were fabricated and measured within a temperature range of 25-135 °C. The resulting 3C-SiC buffer layer improved the insertion loss by approximately 7.3 dB within the SAW resonator and enhanced the temperature stability with TCF = −22 ppm/°C up to 135 °C in comparison to that of TCF = −45 ppm/°C within a temperature range of 25-115 °C of the ZnO/Si structure.     

Ohmic contacts to single-crystalline 3C-SiC films for extreme-environment MEMS applications

This paper describes the ohmic contacts to single-crystalline 3C-SiC thin films heteroepitaxially grown on Si (0 0 1) wafers. In this work, a TiW (titanium-tungsten) film was deposited as a contact material by RF magnetron sputter and annealed through the vacuum and rapid thermal anneal (RTA) process. Contact resistivity between the TiW film and the n-type 3C-SiC substrate was measured by the circular transmission line model (C-TLM) method. The contact phases and interface of the TiW/3C-SiC were evaluated with X-ray diffraction (XRD), scanning electron microscope (SEM) and Auger electron spectroscopy (AES) depth-profiles. The TiW film annealed at 1000 °C for 45 s with the RTA plays an important role in the formation of ohmic contact with the 3C-SiC film and the contact resistance is less than 4.62×10⁻⁴ Ω cm². Moreover, the inter-diffusion at the TiW/3C-SiC interface was not generated during, before and after annealing, and was kept in a stable state. Therefore, the ohmic contact formation technology of single-crystalline 3C-SiC films by using the TiW film is very suitable for high-temperature micro-electro-mechanical system (MEMS) applications.     

Surface acoustic wave characteristics of AlN thin films grown on a polycrystalline 3C-SiC buffer layer

In this study, AlN thin films were deposited on a polycrystalline (poly) 3C-SiC buffer layer for surface acoustic wave (SAW) applications using a pulsed reactive magnetron sputtering system. AFM, XRD and FT-IR were used to analyze structural properties and the morphology of the AlN/3C-SiC thin film. Suitability of the film in SAW applications was investigated by comparing the SAW characteristics of an interdigital transducer (IDT)/AlN/3C-SiC structure with the IDT/AlN/Si structure at 160 MHz in the temperature range 30-150 °C. These experimental results showed that AlN films on the poly (1 1 1) preferred 3C-SiC have dominant c-axis orientation. Furthermore, the film showed improved temperature stability for the SAW device, TCF = −18 ppm/°C. The change in resonance frequency according to temperature was nearly linear. The insertion loss decrease was about 0.033 dB/°C. However, some defects existed in the film, which caused a slight reduction in SAW velocity.     

Characterization of polycrystalline 3C-SiC thin film diodes for extreme environment applications

This paper describes the fabrication and characteristics of polycrystalline (poly) 3C-SiC thin film diodes for extreme environment applications, in which the poly 3C-SiC thin film was deposited onto oxidized Si wafers by APCVD using HMDS as a precursor. In this work, the optimized growth temperature and HMDS flow rate were 1100 °C and 8 sccm, respectively. A Schottky diode with a Au, Al/poly 3C-SiC/SiO₂/Si(n-type) structure was fabricated and its threshold voltage (V_d), breakdown voltage, thickness of depletion layer, and doping concentration (N_D) values were measured as 0.84 V, over 140 V, 61 nm, and 2.7 × 10¹⁹ cm³, respectively. To produce good ohmic contact, Al/3C-SiC were annealed at 300, 400, and 500 °C for 30 min under a vacuum of 5.0 × 10⁻⁶ Torr. The obtained p-n junction diode fabricated by poly 3C-SiC had similar characteristics to a single 3C-SiC p-n junction diode.     

Fabrication of low defect density 3C-SiC on SiO2 structures using wafer bonding techniques

This paper reports on a process to fabricate single-crystal 3C-SiC on SiO₂ structures using a wafer bonding technique. The process uses the bonding of two polished polysilicon surfaces as a means to transfer a heteroepitaxial 3C-SiC film grown on a Si wafer to a thermally oxidized Si wafer. Transfer yields of up to 80% for 4 inch diameter 3C-SiC films have been achieved. Homoepitaxial 3C-SiC films grown on the 3C-SiC on SiO₂ structures have a much lower defect density than conventional 3C-SiC on Si films.     

Fabrication of micro heaters on polycrystalline 3C-SiC suspended membranes for gas sensors and their characteristics

This paper describes the design, fabrication, and characteristics of micro heaters mad on AlN (0.1 μm)/3C-SiC (1 μm) suspended membranes using surface micromachining technology. 3C-SiC and AlN thin films, which have a large energy band gap and very low lattice mismatch, were used for high-temperature environments. A Pt thin film was used as micro heaters and temperature sensor materials. The resistance of the temperature detector (RTD) and the power consumption of the micro heater were measured and calculated. The heater is designed for an operating temperature up to about 800 °C and can be operated at about 500 °C with a power of 312 mW. The thermal coefficient of the resistance (TCR) of fabricated Pt RTD’s is 3174.64 ppm/°C. The thermal distribution measured by IR thermovision is uniform across the membrane surface.     

Diffusional creep induced stress relaxation in thin Cu films on silicon

The results of stress measurements during annealing of thin copper films deposited on 100 μm Si substrates are presented. The stress in thin films was determined by using an optical system for curvature measurements. The annealing experiments were done during thermal cycles of heating and cooling procedures from room temperature up to 400 °C with a rate 10 °C/min. The total thickness of thin films was between 20 and 100 nm. The obtained results showed that the difference between the end and the initial values of the ratio of force to width increases with the thickness of the samples. The initial linear shape of the temperature-stress plots reaches higher temperature values with an increase in film thickness. In order to explain the observations, the dependence of stress on temperature was calculated using the rate of Coble creep. It was found that the theoretical curves reveal the same features as the experimental data. It was concluded that diffusional creep mechanism dominates for thin film of thickness below 100 nm.     

Electrical property dependence on thickness and morphology of nanocrystalline diamond thin films

In this study, we investigate the influence of nanocrystalline diamond (NCD) thin film morphology and thickness on their electrical properties. NCD films are grown on p-type Si substrates with varied thicknesses from 250 to 788 nm. Electrical contacts are formed from combination of Ti/Au metal layers (100 nm thick each). The I-V and breakdown field measurements are used to analyze the electrical properties of metal/NCD/Si sandwich structure. In addition, NCD films are analyzed by scanning electron microscopy and Raman spectroscopy for better interpretation of the I-V measurements.     

Sputtered Ge-on-Si heteroepitaxial pn junctions: Nanostructure, interface morphology and photoelectrical properties

Ge thin films are epitaxially grown onto (1 0 0) Si substrates by DC-Pulsed Magnetron Sputtering. Relaxed single crystalline layers, with slightly misoriented domains are identified by XRD, TEM and HREM. Planar defects and threading dislocations are the relevant lattice imperfections. As-deposited Ge films are p-type without the need for intentional doping, even in the absence of grain boundaries. A pronounced flatness in the near IR absorption spectra is evident, in the absence of strong interfacial strain. This could be traced to a bandgap narrowing effect due to intragap states related to defects in the interfacial region. Photoconductive response around λ = 1.5 μm is flat and an equivalent responsivity R_eff|_{Vbias = −1V} = 1.0088 A/W at λ = 1.5 μm has been estimated.DC-Pulsed Magnetron Sputtering is therefore an attractive solution, deserving further development, to build near-infrared C-MOS compatible photodetectors, particularly suitable for low-speed applications.     

无掩模硅图形衬底上3C-SiC的异质外延生长

采用低压化学气相沉积方法在无掩模的硅图形衬底上异质外延生长3C-SiC.硅图形衬底采用光刻和ICP刻蚀得到.图形由平行长条状沟槽和台面组成,其中沟槽宽度为1～10μm不同间隔,沟槽之间距离为1～10μm不同间隔.对于在不同的沟槽和台面尺寸区域3C-SiC的生长进行了详细研究.采用扫描电镜分别观察了不同区域的生长形貌,分析了图形衬底结构上SiC的生长行为.其中合并生长形成的空气隙结构可以释放由Si和SiC晶格失配引起的应力,从而可以用来解决SiC生长中的晶片翘曲问题,进行厚膜生长.XRD结果表明此无掩模硅图形衬底上得到3C-SiC(111)取向生长.     

Texture of atomic layer deposited ruthenium

Ruthenium films were grown by plasma enhanced atomic layer deposition (ALD) on Si(1 0 0) and ALD TiN. X-ray diffraction (XRD) showed that the as-deposited films on Si(1 0 0) were polycrystalline, on TiN they were (0 0 2) oriented. After annealing at 800 °C for 60 s, all Ru films were strongly (0 0 2) textured and very smooth. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) demonstrated that the lateral grain size of the annealed films was several 100 nm, which was large compared to the 10 nm thickness of the films. No ruthenium silicide was formed by annealing the ALD Ru films on Si(1 0 0). Comparison with sputter deposited films learned that this occurred because the ammonia plasma created a SiO_xN_y reaction barrier layer prior to film growth.     

Non-linear properties of nitride-based nanostructures for optically controlling the speed of light at 1.5 μm

Future bandwidth demand in optical communications requires all-optical devices based on optical non-linear behavior of materials. InN, with a room temperature direct bandgap well below 0.82 eV (1.5 μm) is very attractive for these applications. In this work, we characterize the non-linear optical response and recombination lifetime of the interband transition of InN layers grown on GaN template and Si(1 1 1) by molecular beam epitaxy. Non-linear characterization shows a decrease of the third-order susceptibility, χ⁽³⁾, and an increase of recombination lifetime when decreasing the energy difference between the excitation and the apparent optical band-gap energy of the analysed samples. Taking into account the non-linear characterization, an optically controlled reduction of the speed of light by a factor S=4.2 is obtained for bulk InN at 1.5 μm. The S factor of InN (5 nm)/In_0.7Ga_0.3N (8 nm) multiple quantum well heterostructures at the same operation wavelength is analysed, predicting an increase of this factor of three orders of magnitude. This result would open the possibility of using InN-based heterostructures for all-optical devices applications.     

Si(100)衬底上高质量3C-SiC的改良外延生长

介绍了新近研制出的一种电阻加热式CVD/LPCVD SiC专用制备系统,并利用该系统以SiH4、C2H4和H2作为反应气体在直径为50mm的Si(100)衬底上获得了高质量的3C-SiC外延材料.用X射线衍射和Raman散射技术研究了3C-SiC外延膜的结晶质量,在80～300K的温度范围内利用Van der Pauw方法对1～3μm厚的外延膜的电学特性进行了测试,室温Hall迁移率最高达到470cm2/(V*s),载流子浓度为7.7×1017cm-3.     

Si(100)衬底上高质量3C-SiC的改良外延生长

介绍了新近研制出的一种电阻加热式CVD/LPCVD SiC专用制备系统,并利用该系统以SiH4、C2H4和H2作为反应气体在直径为50mm的Si(100)衬底上获得了高质量的3C-SiC外延材料.用X射线衍射和Raman散射技术研究了3C-SiC外延膜的结晶质量,在80～300K的温度范围内利用Van der Pauw方法对1～3μm厚的外延膜的电学特性进行了测试,室温Hall迁移率最高达到470cm2/(V*s),载流子浓度为7.7×1017cm-3.     

Raman scattering of polycrystalline 3C-SiC film deposited on AlN buffer layer by using CVD with HMDS

This paper presents the Raman scattering characteristics of poly (polycrystalline) 3C-SiC thin films deposited on AlN buffer layer by atmospheric pressure chemical vapor deposition (APCVD) using hexamethyldisilane (MHDS) and carrier gases (Ar+H₂). The Raman spectra of SiC films deposited on AlN layer of before and after annealing were investigated according to the growth temperature of 3C-SiC. Two strong Raman peaks, which mean that poly 3C-SiC admixed with nanoparticle graphite, were measured in them. The biaxial stress of poly 3C-SiC/AlN was calculated as 896 MPa from the Raman shifts of 3C-SiC deposited at 1180 °C on AlN of after annealing.     

The microwave properties of Li doped 0.7(Ba,Sr)TiO3-0.3MgO thick film interdigital capacitors on the alumina substrates

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO₃ materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current-voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (dρ/dT) of 6.11 × 10⁸ Ω cm/°C, then film showed negative temperature coefficient of resistivity (dρ/dT) of −1.74 × 10⁸ Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.     

Insulating substrates for cubic GaN-based HFETs

The growth of cubic group III-nitrides is a direct way to eliminate polarization effects, which inherently limits the fabrication of normally off heterojunction field-effect transistors (HFETs) in the GaN technology. However, for the achievement of electronic devices with cubic nitrides an important precondition is the availability of a high-resistive substrate or GaN buffer layer with zinc-blende crystal structure. We investigated the applicability of carbonized high resistance Si (0 0 1)-substrates and thick conductive free-standing 3C-SiC (1 0 0) substrates with an Ar⁺-ion-damaged surface layer for this purpose and studied the use of carbon-doped GaN buffer layers for electrical insulation. We found that Ar-implantation of 3C-SiC is an appropriate alternative to fabricate insulation layer for cubic GaN (c-GaN) growth and that C-doped GaN buffers introduce non-linear I-V characteristics. The structural properties of c-GaN on Ar-implanted 3C-SiC are comparable to GaN on untreated 3C-SiC whereas on carbonized Si substrates an increase of dislocation density and surface roughness is observed.     

Strain status in ZnO film on sapphire substrate with a GaN buffer layer grown by metal-source vapor phase epitaxy

ZnO film of 8 μm thickness was grown on a sapphire (0 0 1) substrate with a GaN buffer layer by a novel growth technique called metal-source vapor phase epitaxy (MVPE). The surface of ZnO film measured by scanning electron microscope (SEM) is smooth and shows many regular hexagonal features. The full width at half maximum (FWHM) of ZnO(0 0 2) and (1 0 2) ω-scan rocking curves are 119 and 202 arcsec, corresponding a high crystal quality. The status of the strain in ZnO thick film was particularly analyzed by X-ray diffraction (XRD) ω-2θ scanning. The results show that the strain in ZnO film is compressive, which is also supported by Raman scattering spectroscopy. The compressive strain can solve the cracking problem in the quick growth of ZnO thick film.     

Heterojunction diodes in 3C-SiC/Si system grown by reactive magnetron sputtering: Effects of growth temperature on diode rectification and breakdown

3C-SiC/Si heterojunction diodes were prepared by reactive magnetron sputtering of pure Si in CH₄-Ar discharge on Si(111) substrates kept at temperatures (T_s) ranging from 800 to 1000°C. A good diode rectification process started for films grown at T_s≤900°C. Heterojunction diodes grown at T_s = 850°C showed the best performance with a saturation current density of 2.4 × 10⁻⁴ A cm⁻². Diode reverse breakdown was obtained at a voltage of −110 V. The doping concentration (N_d) of the 3C-SiC films was calculated from 1/C² vs V plot to be 3 × 10¹⁵ cm⁻³. Band offset values obtained were −0.27 and 1.35 eV for the conduction and valence band, respectively. X-ray diffraction analysis revealed the film grown at T_s = 850°C to be single-phase 3C-SiC. The full width at half maximum of the 3C-SiC(111) peak was only 0.25 degree. Cross-sectional transmission electron microscopy showed the film to be highly (111)-oriented with an epitaxial columnar structure of double positioning domain boundaries.     

Unusual defects in silicon carbide thin films grown by multiple or interrupted growth technique

This paper discusses the growth and characterization of 3C-SiC films on Si (1 0 0) and (1 1 1) substrates using hexamethyldisilane (HMDS) as the source material in a resistance-heated furnace as well as the formation and microstructure of various types of unusual defects. Apart from common triangular and square voids, some unusual shaped voids like hexagonal, truncated octahedron, etc. and some irregular features (like hockey stick or pipes) were observed regularly, which are related to voids. SiC whiskers and wires with a wide range of diameters (nm to μm) were formed inside cracked regions as well as within voids. Optical microscopy, scanning electron microscopy (SEM) and Raman spectroscopy were used to study these features.