Silicon carbide (SiC) is widely recognized as the leading candidate to replace silicon in micro-electro-mechanical systems devices operating in harsh environments. In this work, cantilevers and bridges in SiC are designed, fabricated and evaluated between room temperature (RT) and 600 °C. The active material is a cubic poly-SiC film deposited on a poly-Si layer which is separated from the Si substrate by a thermal oxide. From surface profiling and optical observations, it is deduced that an average residual strain of +5 × 10−4 is present in the 2.7 µm thick film, with a gradient of 2.5 × 10−4 µm−1. The structures are excited either mechanically or electrostatically. Their resonance frequency is measured by laser Doppler velocimetry and used to derive the Young's modulus and residual stress in the heteroepitaxial layer (330± 45 GPa and 200± 20 MPa, respectively). The temperature coefficient of Young's modulus is found to be −53± 2 ppm K−1 in the range RT to ∼ 300 °C, while an analytical expression is given for the temperature dependence of the Young's modulus between RT and 500 °C. The residual tensile stress is found to depend on temperature in a complex manner.

Experimental evidence is given for boron (B) enhanced diffusion of nitrogen (N) in ion-implanted 4H silicon carbide (4H-SiC), when a nitrogen implant is co-doped within an existing boron p-type well. The co-implanted nitrogen is shown to diffuse continuously with time when samples are annealed at 1600 °C—with little movement of the boron p-well implant profile. An effective nitrogen in boron diffusivity at 1600 °C is determined to be at least 60 times larger than that of a mono-doped nitrogen implant.

Articles you may be interested inA methodology to identify and quantify mobility-reducing defects in 4H-silicon carbide power metal-oxidesemiconductor field-effect transistors Diffusion of boron in 6H and 4H SiC coimplanted with boron and nitrogen ions A field enhanced diffusion ͑FED͒ model is proposed for the observed phenomenon of dopant migration within 4H silicon carbide ͑4H-SiC͒ during high temperature annealing. The proposed FED model is based on the combined effects of both dopant diffusion and the in-built p -n junction electric field gradients found within the doped substrate resulting from the presence of the substrate dopants. Measured as-implanted dopant concentration profile data prior to high temperature annealing are utilized as input data for the proposed FED model. The resultant FED profile predictions of the proposed model during annealing are shown to be in excellent agreement with experimental findings. Parameters are extracted using the FED model simulation for the high temperature ionic diffusivity and ionic field mobility for nitrogen dopant in boron co-doped 4H-SiC. The extracted values for the ionic diffusivity and the ionic mobility of the nitrogen donor in boron co-doped 4H-SiC found using the model are 7.2ϫ10 Ϫ15 cm 2 s Ϫ1 and 1.6ϫ10 Ϫ13 cm 2 V Ϫ1 s Ϫ1 , respectively.

Zener diodes are widely used in electrical barriers to protect equipment operating in a potentially explosive atmosphere. Although normally not conducting, the zeners must have a high power rating so that their junction temperature meets safety factors when shunting the maximum fuse current. This often requires two or three lower voltage commercial zeners connected in series. Silicon carbide diodes have much higher thermal conductivity and maximum allowed junction temperature, so it should be possible to use one SiC zener in the place of two or three commercial diodes and/or allow use of higher fuse ratings. Low voltage SiC Zener diodes were fabricated and tested to evaluate potential benefits of their application as a component of intrinsically safe barriers. The diodes demonstrated mixed avalanche-tunnel breakdown at reverse bias voltages of 23 V with positive temperature coefficients of breakdown voltages of about 0.4 mV/°C. The diodes with mesa area of 4×10-4cm2 had maximum DC Zener current of 1.2 A and were capable of operating at ambient temperatures up to 500°C.

Experimental evidence is given for a newly observed surface morphological phenomenon (step bunch bleed) and its implications for device fabrication constraints in ion implanted 4H-silicon carbide (4H-SiC) are discussed.Step bunch bleed is the result of surface step bunching spreading during a high-temperature anneal process to bridge closely adjacent patterned lithographic features where step bunching would otherwise not occur. It is found that the phenomenon of step bunch bleed could limit the minimum practical lithographic distance between adjacent nitrogen implants within a boron well structure in 4H-SiC to the order of 1 µm-depending on the crystallographic orientation of the implant pattern.