Si Carrier Research Articles

The use of Si carriers for aerosol particle collection and subsequent elemental analysis by total-reflection X-ray fluorescence spectrometry

The adoption of polished Si carriers was studied for the sensitive elemental analysis of aerosol particles using total-reflection X-ray fluorescence (TXRF) spectrometry. The surface roughness of the Si carrier measured by atomic force microscopy was found to be smaller than those of glassy carbon and quartz glass carriers, which are commonly used for TXRF analysis. The detection limits of elements for the Si carrier were superior to those for the glassy carbon and the quartz glass carriers, presumably due to its smaller surface roughness. For example, the detection limit of Sr for the Si carrier was 9 pg, which was 100 times and 3 times lower than those for the glassy carbon and the quartz glass carriers, respectively. The Si carriers could be successfully applied to the direct aerosol particle collection by impaction and the subsequent elemental analysis by TXRF. From the results of the elemental analysis of aerosol particles, the variations in the concentrations of K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn Sr and Pb with time could be clarified.

Effect of band alignment and density of states on the collector current in p-Si/n-Si/sub 1-y/C/sub y//p-Si HBTs

p-Si/n-Si/sub 1-y/C/sub y//p-Si heterojunction bipolar transistors with varying carbon fractions in the base were grown by rapid thermal chemical vapor deposition (RTCVD), to better understand the potential of Si/sub 1-y/C/sub y/ in enhancing the performance of Si-based bipolar technology. The band line-up issues which make Si/sub 1-y/C/sub y/ a desirable choice for forming the base region in a p-n-p HBT are discussed. Electrical measurements performed on the p-Si/n-Si/sub 1-y/C/sub y//p-Si HBTs (y=0.6, 0.8 at.%) are used to extract important information regarding the electronic properties of the Si/Si/sub 1-y/C/sub y/ material system, e.g., the bandgap reduction in Si/sub 1-y/C/sub y/ compared to Si and minority carrier recombination lifetime in Si/sub 1-y/C/sub y/. Temperature dependent measurements of the collector current were performed to extract the bandgap narrowing at the Si/Si/sub 1-y/C/sub y/ heterojunction. This paper includes a detailed analysis of the impact of heavy doping and reduced density of states in Si/sub 1-y/C/sub y/ compared to Si on the extraction of the energy bandgap offset, and on the collector current of p-n-p HBTs. The impact of the reduced density of states on the design of p-n-p Si/Si/sub 1-y/C/sub y/ HBTs is discussed. The measured value of the energy band offset is (65 meV/at.% C) very close to previously measured values of the conduction band offset at the Si/Si/sub 1-y/C/sub y/ heterojunction. The results are thus consistent with a band line-up at the Si/Si/sub 1-y/C/sub y/ interface that is dominated by a conduction band offset with little if any valence band offset.

Precision techniques for whole wafer dicing and thinning of superconducting mixer circuits

Present designs for millimeter and submillimeter superconducting mixer circuits often require finished quartz wafer thicknesses from a few mils to less than a mil. Typically this is accomplished by first dicing the wafer into individual chips and then thinning each chip separately. In our new process the entire wafer is first diced; however, the cuts are only made two mils deeper than the desired finished chip thickness. An ultra-flat Si wafer is prepared with a 5 /spl mu/m thick Apiezon-W black wax coating on both sides. The quartz wafer is mounted to the Si carrier, cuts side down, which is itself mounted to a stainless steel lapping block. The of block/Si/quartz is then placed in a tool designed to permit compression of the sandwich to 30 psi at 145C. In this process the quartz wafer is positioned flat with respect to the Si wafer to better than +/-2.5 /spl mu/m. The stack is then lapped and polished through the backside of the wafer, into the cuts to the desired wafer thickness to better than +/-5 /spl mu/m. The Si/quartz bilayer is subsequently removed from the block resulting in a fully diced and thinned quartz wafer.

W ohmic contact for highly doped n-type GaN films

Ohmic contacts with low resistance and low barrier height were fabricated on n-type GaN films using W metallization. The n-type GaN films were grown by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with Si as the dopant. Ohmic characteristics were studied for GaN films with Si carrier concentration varying from 1.4×10 17 to 1.8×10 19 cm −3. The specific contact resistivity were reduced with increasing Si-doping concentration on as-deposited W/GaN films, and the lowest value was 3.6×10 −4 Ωcm 2 on n-type GaN with a concentration of 1.8×10 19 cm −3. After rapid thermal annealing (RTA) treatment on W/GaN films at 1000°C for 30 s, the specific contact resistivity were reduced to 1×10 −4 Ωcm 2. The W metal on n-type GaN films, show that good thermal stability varied the annealing temperatures. The barrier height of as-deposited W metal on GaN is calculated to be 0.058 eV.

Laser ablation threshold determination by photoelectric emission

Laser-induced surface damage introduces a dramatic change in the photoelectric properties of metallic and semiconductor substrates. Hence, by varying the applied laser intensity, ultra-short- pulsed laser-induced photoemission (in the mono- or multiphotonic regime according to the applied wavelength) can be used to monitor in situ surface structural changes. Results for a model system (thin diamond-like carbon (DLC) layer on an Si carrier) are presented, where, after ablation of the DLC layer, we observed a rapid increase in the photoelectric contribution from the underlying substrate. High-sensitivity measurements are presented for Au and W substrates where due to laser- induced damage within the escape depth of electrons and because of the apparition of ionized species upon ablation, the measured charge can indicate the onset of surface damage. Results are presented for various wavelengths (213 nm, 266 nm and 532 nm) and discussed in the light of previous results of threshold measurements obtained by optical methods.

Electron-transport simulation in silicon including anisotropic phonon scattering rate.

The influence of anisotropic phonon scattering on Si carrier transport properties was investigated at low field using the phonon-scattering-rate models given by P(${\mathbf{k}}_{\mathit{i}}$,${\mathbf{k}}_{\mathit{f}}$), P(${\mathbf{k}}_{\mathit{i}}$), and P(E). The transient drift velocity in silicon was found to be slightly modified with the anisotropic nature of the phonon scattering rates, while no difference was observed in the steady-state velocity. The magnitude of the velocity overshoot is slightly reduced by using the anisotropic phonon scattering rates based on a rigid pseudo-ion model.

Electrodes for Functional Neuralmuscular Stimulation

AbstractElectrodes for FNS were fabricated by photolithographic techniques from foils of Mo, Ta, and stainless steel with lateral dimensions of 1–3 mm and thickness of about 50 μm. More recent designs have utilized a Si carrier with either a Pt or diffused Si track terminated by Au electrodes. Biocompatibility studies conducted on frogs and rabbits indicate good stability of electrodes coated with SiO by plasma deposition. Carriers did not move after implantation and did not show signs of corrosion. The diffused Si design is now preferred since electrode tracks are sub-surface, tracks may be electrically and biologically insulated by SiO2, all fabrication steps are compatible with standard integrated circuit processing such that electronics may be integrated on the carrier with the electrode tracks, and small dimensions are easily attained.