Metal-Insulator-Semiconductor Technique

Chemical and physical processing techniques for ferroelectric thin films have undergone explosive advancement in the past few years (see Ref. 1, for example). The use of PZT (PbZri- cTi c03) family ferroelectrics in the nonvolatile and dynamic random access memory applications present potentially large markets [2]. Other thin-film devices based on a wide variety of ferroelectrics have also been explored. These include multilayer thin-film capacitors [3], piezoelectric or electroacoustic transducer and piezoelectric actuators [4-6], piezoelectric ultrasonic micromotors [7], high-frequency surface acoustic devices [8,9], pyroelectric intrared (IR) detectors [10-12], ferroelectric/photoconduc-tive displays [13], electrooptic waveguide devices or optical modulators [14], and ferroelectric gate and metal/insulator/semiconductor transistor (MIST) devices [15,16]. 

Another impedance-based imaging technique for laterally resolved characterization of thin films or electrochemical systems is Scanning Photo-induced Impedance Microscopy (SPIM) [44]. It is based on photocurrent measurements at field-effect structures. In their simplest arrangement, field-effect structures consist of a semiconductor substrate with a thin insulator, and a gate electrode. This gate electrode can be a metal film resulting in the structure Metal Insulator Semiconductor (MIS) or, alternatively. Electrolyte Insulator Semiconductor structures are used, in which the electrolyte is in direct contact with the insulator, and a reference electrode is required to fulfill the function of the gate electrode. 

Pilippini D, Lundstrom I (2003) Chemical images generated by large area homogeneous illumination of metal-insulator-semiconductor structures. Appl Phys Lett 82 3791-3793 Pilippini D, Andersson T, Svensson S, Lundstrom I (2003) Microplate based biosensing with a computer screen aided technique. Biosens Bioelectron 19 35-41... 

Deposition plays an important role during all processes of microfabrication. Deposition techniques allow deposition of large variety of materials, that is, metals, insulators, semiconductors, polymers, proteins, and so on. Some of the common additive techniques are discussed in the following section. 

The process of GaAs oxidation is so complex that even after many years of work there are important issues that are still a matter of controversy. Consequently, the GaAs metal insulator semiconductor field effect transistor (MISEET) technology did not develop very weU since the electronic passivation of GaAs is not fully resolved. The challenges in the fabrication of high quality oxide layers on GaAs stimulate researchers to find out the most suitable techniques and conditions to solve the interface-related problems. 

Molecular beam epitaxy (MBE) is an expensive yet widely used technique for producing epitaxial layers of metals, insulators and III-V and II-VI based semiconductors, both at the research and the industrial production level (Herman, 1996). It consists of deposition of molecular beams of atoms or clusters of atoms, which are produced by heating up a solid source, onto a heated crystalline substrate in ultra-high vacuum. MBE is characterized by low growth temperatures and low growth rates and thus enables producing high-precision epitaxial structures with monolayer... 

The ion controlled diode was an initial attempt to isolate the active electronics from the chemical solution by producing a metallic-like via that allows the isolation of the chemically sensitive region from an area where electronic components could be deposited (41,42). However, the limited precision of the non-standard microfabrication techniques made this process difficult and costly. Since this device is still essentially a capacitive membrane-insulator-semiconductor structure like the chemfet, the same problems of hermetic isolation of the gate remain. 

Sputtering is a standard process in materials science and it has required fairly minor adaptation for its use in fluidic device fabrication. Hence, few papers specifically deal with sputtering for microfluidics most authors mention sputtering as a technique employed in a rather brief manner. A non-exhaustive overview of different sputtering applications is given in Table 2. Many more metals, alloys, semiconductors, and insulators can be sputtered than are listed in this table however, they are beyond the scope of this article. 

In the processing of integrated circuits, silicon dioxide (SiOa) can be used as a mask during ion implantation or diffusion of impurity into silicon, for passivation, for protection of the device surface, as interlayers for multilevel metallization, or as the active insulating material — the gate oxide film in metal-oxide-semiconductor (MOS) devices [1, 2], At the present time, several methods have been developed for the formation of Si02 layers, including thermal and chemical oxidation, anodization in electrolyte solutions, and various chemical vapor deposition (CVD) techniques [2, 3],... 

The application of LEED is limited to ultrahigh vacuum (UHV) conditions because of the character of the probe and its high surface sensitivity. The main application is the study of single crystal metal and semiconductor surfaces, and adsorption on these surfaces. Study of surfaces of thin insulator films is also possible. Recently, the application extends to study the surface structure of quasicrystals. LEED is widely applied to determine the symmetry and periodicity of surface structures and thus to identify reconstructions and adsorbate phases by observing the diffraction pattern. It is also a technique for quantitative surface structure analysis. LEED is also appHed as the quantitative determination of thermal vibrations at surfaces. 

Real-world structured surfaces for superhydrophobic electrowetting range from geometrically uniform like those in Figs Id and 2a, to randomly oriented fiberlike structures. Most demonstrated works include a composite dielectric approach. In this composite approach the structured electrode is first insulated with a conventional dielectric such as a metal or semiconductor oxide. The composite dielectric is then completed with a plasma deposited fluorocarbon or solution deposited flu-oropolymer in order to provide adequate hydrophobicity for a stable Cassie state. A brief review of techniques to create superhydrophobic electrowetting surfaces is provided below. The demonstrated structures vary substantially in geometry and materials, however, electrowetting results are somewhat similar across all platforms. 

---