Jeffrey Bernard Fortin

Scalable vertical diaphragm pressure sensors: device and process Design, Design for packaging

We present a design, process How, and packaging scheme for a novel three-dimensional capacitive microelectromechanical systems pressure sensor [1], [10]. These sensors present a paradigm shift in pressure sensor technology. They contain an array of vertical diaphragms perpendicular to the wafer plane where each pair of diaphragms requires orders of magnitude lower footprint than traditional in-plane sensors. The sensor can be arrayed or scaled up for increased sensitivity and can be absolute, gauge or differential. Fabrication requires 2-4 masks, depending on process How and has been greatly simplified, without reduction in performance, for high yield and low cost. Multiple geometries have been modeled with sensitivities reaching several fF/kPa and temperature coefficient of sensitivity better than conventional devices. Pressure and electrical ports are individually interchangeable between front and back sides. This allows for a simple design that has only Si facing the sensing environment and the electrical connections on the backside, thus enabling simple packaging for both pressure and electrical ports.

Deposition Kinetics for Polymerization via the Gorham Route

It is known to those familiar with parylene that it is has very unique deposition kinetics. The deposition rate increases as the substrate temperature is decreased, which is the opposite of most CVD reactions. The deposition rate increases as the monomer pressure in the chamber is increased, which is more typical of a CVD reaction. It is also known that there is a minimum pressure below which no deposition occurs. This pressure increases (decreases) as substrate temperature increases (decreases). Before more information is presented on parylene kinetic models it is important to have an overview of CVD kinetics in general.

3-dimensional scalable pressure sensors: device and process design

We present the design, process flow and packaging scheme for a novel 3D capacitive MEMS pressure sensor. These sensors present a paradigm shift in pressure sensor technology. They contain an array of vertical diaphragms perpendicular to the wafer plane where each pair of diaphragms requires orders of magnitude lower footprint than traditional in-plane sensors. The sensor can be arrayed or scaled up for increased sensitivity and can be absolute, gauge or differential. Fabrication requires 2-4 masks depending on process flow and has been greatly simplified, without reduction in performance, for high yield and low cost. Multiple geometries have been modeled with sensitivities reaching several fF/kPa and temperature characteristics better than conventional devices. Pressure and electrical ports are individually interchangeable between front and back sides. This allows for a simple design that has only Si facing the sensing environment and the electrical connections on the backside.

Step-by-Step Guide to Depositing Parylene

In this chapter we will present a step-by-step procedure that one would use to deposit parylene using a typical deposition system. The steps for your deposition will most likely deviate from these but they are not meant to be followed exactly but more to give the general understanding of the process of parylene deposition.

Parylene-N Precursor Chemistry

The starting material for the deposition of parylene film is a dimer in the form of a white powder. This dimer can be purchased through a number of companies in the US and abroad, including Para Tech Coating, Inc. (visit http://www.parylene.com) and Speedline Technologies (visit http://www.scscookson.com). The dimer for parylene-N, which is also called di-para-xylylene and [2,2]paracyclophane was first reported by Brown as a product of xylene pyrolysis and later was synthesized with high yield by Cram [77]. According to Beach et al., there are two common routes to the synthesis of the dimer, di-para-xylyene; the direct pyrolysis of p-xylene and the 1,6 Hoffman elimination of amine from a quaternary ammonium hydroxide [1]. Beach et al. also state that purification of the dimer is often accomplished by recrystallization from the solvent xylene.

Other CVD Polymers

In addition to the Parylene family, there are several classes of polymer that have been shown to form thin film by evaporation or via chemical vapor deposition routes. Among them, rigid-rod aromatic polymers, due to their structure, possess several very attractive properties that have a great potential for many applications such as protective coating. They possess high thermal stability, high glass transition temperature, high hardness, insolubility to common solvents, and oxidation resistance. Although these films possess very desirable properties, only limited work has been reported in this area of research. In this Chapter, we will describe a selective group of polymeric films deposited via different types of vapor deposition techniques.