James H. Logsdon

A bridge-type piezoresistive accelerometer using merged epitaxial lateral overgrowth for thin silicon beam formation

Abstract Merged epitaxial lateral overgrowth (MELO) of silicon has been used to form 10 μm ± 0.5 μm thick, 420 μm long, and 170 μm wide single-crystal silicon beams for a four-bridge piezoresistive accelerometer. Buried SiO2 stripes are used to produce the near-perfect backside etch-stop for the silicon membrane, while the topside thickness control is established by the growth rate of 0.1 μm min−1. The MELO membrane technique produces an accelerometer that has low-doped high-quality single-crystal silicon beams. The measured sensitivity is 287 μV V−1 g−1, which is about twice that for a similar device, and the non-linearity is less than 4% up to 30g of acceleration.

A comparison of different deposition techniques for fabricating polysilicon contacted emitter bipolar transistors

Four methods for fabricating polysilicon contacted bipolar junction transistors (BJT’s) have been investigated. In the first method polysilicon was deposited using low‐pressure chemical vapor deposition (LPCVD) at 620 °C. In the remaining three methods a‐Si was first deposited and then recrystallized to form polysilicon. In the second method a‐Si was deposited using LPCVD at 580 °C. The third method used plasma‐enhanced chemical vapor deposition (PECVD) to deposit a‐Si:H. The fourth method involved a plasma etch with argon or hydrogen prior to deposition of a‐Si:H using PECVD. The results indicated that using the PECVD method for depositing a‐Si:H without any prior plasma‐etch step and recrystallizing it to form polysilicon resulted in the highest current gain (β) enhancement of 3.5 and also allowed the reduction of the polysilicon anneal temperature down to 800 or 900 °C from 1000 °C. The compactness in the spread of the peak β values for the devices fabricated using this technique also reflects its abil...

A novel method of forming a thin single crystal silicon diaphragm with precise thickness for potential use in fabricating micromechanical sensors using merged epitaxial lateral overgrowth

A novel epitaxial growth and micromachining technology were used for form a thin single-crystal silicon diaphragm for micromechanical sensors. Merged epitaxial lateral overgrowth (MELO) of silicon and SiO/sub 2/ etch-stop technology were successfully used to fabricate a diaphragm with a precise thickness. Its implementation to the formation of a large thin diaphragm is demonstrated. The silicon epitaxial growth rate is the only controlling parameter to define the diaphragm thickness. An average growth uniformity of the MELO film across the three-inch wafers was determined to be less than 5%. However, the average percentage variation of the growth at the same position on the wafer, from wafer to wafer in a single run, was measured to be within 2%. Diaphragms of 9+or-0.05 mu m thick and more than 200 mu m wide and 1000 mu m long were successfully fabricated using this technique.<<ETX>>