Design and Fabrication of a Novel Poly-Si Microhotplate with Heat Compensation Structure

I Microhotplates are critical devices in various MEMS sensors that could provide appropriate operating temperatures. In this paper, a novel design of poly-Si membrane microhotplates with a heat compensation structure was reported. The main objective of this work was to design and fabricate the poly-Si microhotplate, and the thermal and electrical performance of the microhotplates were also investigated. The poly-Si resistive heater was deposited by LPCVD, and phosphorous doping was applied by in situ doping process to reduce the resistance of poly-Si. In order to obtain a uniform temperature distribution, a series of S-shaped compensation structures were fabricated at the edge of the resistive heater. LPCVD SiNx layers deposited on both sides of poly-Si were used as both the mechanical supporting layer and the electrical isolation layer. The Pt electrode was fabricated on the top of the microhotplate for temperature detection. The area of the heating membrane was 1 mm × 1 mm. Various parameters of the different size devices were simulated and measured, including temperature distribution, power consumption, thermal expansion and response time. The simulation and electrical-thermal measurement results were reported. For microhotplates with a heat compensation structure, the membrane temperature reached 811.7 °C when the applied voltage was 5.5 V at a heating power of 148.3 mW. A 3.8 V DC voltage was applied to measure the temperature distribution; the maximum temperature was 397.6 °C, and the area where the temperature reached 90% covered about 73.8% when the applied voltage was 3.8 V at a heating power of 70.8 mW. The heating response time was 17 ms while the microhotplate was heated to 400 °C from room temperature, and the cooling response time was 32 ms while the device was recovered to room temperature. This microhotplate has many advantages, such as uniform temperature distribution, low power consumption and fast response, which are suitable for MEMS gas sensors, humidity sensors, gas flow sensors, etc.

Effect of the Graded Silicon Content in SRN/SRO Multilayer Structures on the Si Nanocrystals and Si Nanopyramids Formation and Their Photoluminescence Response

Two multilayer (ML) structures, composed of five layers of silicon-rich oxide (SRO) with different Si contents and a sixth layer of silicon-rich nitride (SRN), were deposited by low pressure chemical vapor deposition. These SRN/SRO MLs were thermally annealed at 1100 °C for 180 min in ambient N₂ to induce the formation of Si nanostructures. For the first ML structure (MLA), the excess Si in each SRO layer was about 10.7 ± 0.6, 9.1 ± 0.4, 8.0 ± 0.2, 9.1 ± 0.3 and 9.7 ± 0.4 at.%, respectively. For the second ML structure (MLB), the excess Si was about 8.3 ± 0.2, 10.8 ± 0.4, 13.6 ± 1.2, 9.8 ± 0.4 and 8.7 ± 0.1 at.%, respectively. Si nanopyramids (Si-NPs) were formed in the SRO/Si substrate interface when the SRO layer with the highest excess silicon (10.7 at.%) was deposited next to the MLA substrate. The height, base and density of the Si-NPs was about 2–8 nm, 8–26 nm and ~6 × 10¹¹ cm⁻², respectively. In addition, Si nanocrystals (Si-ncs) with a mean size of between 3.95 ± 0.20 nm and 2.86 ± 0.81 nm were observed for the subsequent SRO layers. Meanwhile, Si-NPs were not observed when the excess Si in the SRO film next to the Si-substrate decreased to 8.3 ± 0.2 at.% (MLB), indicating that there existed a specific amount of excess Si for their formation. Si-ncs with mean size of 2.87 ± 0.73 nm and 3.72 ± 1.03 nm were observed for MLB, depending on the amount of excess Si in the SRO film. An enhanced photoluminescence (PL) emission (eight-fold more) was observed in MLA as compared to MLB due to the presence of the Si-NPs. Therefore, the influence of graded silicon content in SRN/SRO multilayer structures on the formation of Si-NPs and Si-ncs, and their relation to the PL emission, was analyzed.

Vertically-Aligned Multi-Walled Carbon Nano Tube Pillars with Various Diameters under Compression: Pristine and NbTiN Coated

In this paper, the compressive stress of pristine and coated vertically-aligned (VA) multi-walled (MW) carbon nanotube (CNT) pillars were investigated using flat-punch nano-indentation. VA-MWCNT pillars of various diameters (30-150 µm) grown by low-pressure chemical vapor deposition on silicon wafer. A conformal brittle coating of niobium-titanium-nitride with high superconductivity temperature was deposited on the VA-MWCNT pillars using atomic layer deposition. The coating together with the pillars could form a superconductive vertical interconnect. The indentation tests showed foam-like behavior of pristine CNTs and ceramic-like fracture of conformal coated CNTs. The compressive strength and the elastic modulus for pristine CNTs could be divided into three regimes of linear elastic, oscillatory plateau, and exponential densification. The elastic modulus of pristine CNTs increased for a smaller pillar diameter. The response of the coated VA-MWCNTs depended on the diffusion depth of the coating in the pillar and their elastic modulus increased with pillar diameter due to the higher sidewall area. Tuning the material properties by conformal coating on various diameter pillars enhanced the mechanical performance and the vertical interconnect access (via) reliability. The results could be useful for quantum computing applications that require high-density superconducting vertical interconnects and reliable operation at reduced temperatures.

Superior Robust Ultrathin Single-Crystalline Silicon Carbide Membrane as a Versatile Platform for Biological Applications

Micromachined membranes are promising platforms for cell culture thanks to their miniaturization and integration capabilities. Possessing chemical inertness, biocompatibility, and integration, silicon carbide (SiC) membranes have attracted great interest toward biological applications. In this paper, we present the batch fabrication, mechanical characterizations, and cell culture demonstration of robust ultrathin epitaxial deposited SiC membranes. The as-fabricated ultrathin SiC membranes, with an ultrahigh aspect ratio (length/thickness) of up to 20 000, possess high a fracture strength up to 2.95 GPa and deformation up to 50 μm. A high optical transmittance of above 80% at visible wavelengths was obtained for 50 nm membranes. The as-fabricated membranes were experimentally demonstrated as an excellent substrate platform for bio-MEMS/NEMS cell culture with the cell viability rate of more than 92% after 72 h. The ultrathin SiC membrane is promising for in vitro observations/imaging of bio-objects with an extremely short optical access.

Gate bias-dependent junction characteristics of silicon nanowires suspended between polysilicon electrodes

Realistic integration of 1D materials into future nanodevices is limited by the lack of a manipulation process that allows a large number of nanowires to be arranged into an integrated circuit. In this work, we have grown Si nanowire bridges using a thin-film catalyst in a batch process at 200 °C and characterized the produced devices consisting of a p⁺-Si contact electrode, a suspended Si nanochannel, and a polysilicon contact electrode. Both the electrodes and connecting lines are made of Si-based materials by conventional low-pressure chemical vapor deposition. The results indicate that these devices can act as gate-controllable Schottky diodes in integrated nanocircuits.