Silicon-based thin-film electrodes

Iridium oxide films (IROF) were also fabricated on silicon-based thin-film platinum microelectrodes. These electrodes can also measure the pH of the test solution with high sensitivity by intercalating the protons into their structure." ... 

This book is devoted to the properties, preparation and applications of zinc oxide (ZnO) as an transparent electrode material. It focuses on ZnO for thin film solar cell applications and hopefully inspires also readers from related fields. The book is structured into three parts to serve both as an overview as well as a data collection for students, engineers and scientists. The first part, Chaps. 1-4, provide an overview of the application and fundamental material properties of ZnO films and their surface and interfaces properties. Chaps. 5-7 review thin film deposition techniques applied for ZnO preparation on lab scale but also for large area production. Finally, Chaps. 8 and 9 are devoted to applications of ZnO in silicon- and chalcopyrite-based thin film solar cells, respectively. One should note that the application of CVD grown ZnO in silicon thin film cells is discussed earlier in Chap. 6. 

N.-S. Choi, K. H. Yew, H. Kim, S.-S. Kim, W.-U. Choi, J. Power Sources 2007,172,404 09. Surface layer formed on silicon thin-film electrode in lithium bis(oxalato) borate-based electrolyte. 

Choi et al. [118] compared the effect of two different lithium salts on the cycling performance of a 200-nm silicon thin-film electrode. The electrolytes tested were 1.3-M LiPFs in EC/DEC (3 7 by vol) and 0.7-M lithium bis(oxalato) borate (LiBOB) in the same solvent mixture. They found that the LiBOB-based electrolyte markedly improved the discharge capacity retentirm of the lithium-silicon half-cell, over the LiPFs-based electrolyte. The surface layer on the silicon electrode in the LiBOB-based electrolyte was less porous and effectively limited the formation of electro-chemically inactive silicon phases. The capacity fading of the lithium-silicon... 

A hybrid BCB-silicon neural implant with embedded microfluidic channels has been fabricated and tested in acute recordings [70]. A thin layer of silicon was used to add mechanical stiffness to the implant. The fabrication process is based on SOI technology, where the device layer of the wafer was the 2-, 5-, or 10-iim silicon backbone of the BCB structure. The microfluidic channels were made with a sacrificial photoresist layer. Cytotoxicity tests of BCB have demonstrated its biocompatibility in glial and fibroblast cell culture [71] and using brain slice culture [72]. A summary of several microfabricated thin-film electrodes is presented in Table 1. 

Metal oxide semiconductor field-effect transistors (MOSFETs) are field effect transistors with a thin film of silicon dioxide between the gate electrode and the semiconductor. The charge on the silicon dioxide controls the size of the depletion zone in the polype semiconductor. MOSFETs are easier to mass produce and are used in integrated circuits and microprocessors for computers and in amplifiers for cassette players. Traditionally, transistors have been silicon based but a recent development is field-effect transistors based on organic materials. 

An early attempt to make a real electrochemical sensor based on a molecularly imprinted methacrylate polymer utilised conductometric measurements on a field-effect capacitor [76]. A thin film of phenylalanine anilide-imprinted MAA-EDMA copolymer was deposited on the surface of semiconducting p-type silicon and covered with a perforated platinum electrode. An AC potential was applied between this electrode and an aluminium electrode on the back side of the semiconductor and the capacitance measured as a function of the potential when the device was exposed to the analyte in ethanol. The print molecule could be distinguished from phenylalanine but not from tyrosine anilide and the results were very variable between devices, which was attributed to difficulties in the film production. The mechanism by which analyte bound to the polymer might influence the capacitance is again rather unclear. 

The properties of the dual-film electrode were characterized by in situ Fourier transform infrared (FTIR) reflection absorption spectroscopy [3]. The FTIR spectrometer used was a Shimadzu FTIR-8100M equipped with a wide-band mercury cadmium teluride (MCT) detector cooled with liquid nitrogen. In situ FTIR measurements were carried out in a spectroelectro-chemical cell in which the dual-film electrode was pushed against an IR transparent silicon window to form a thin layer of solution. A total of 100 interferometric scans was accumulated with the electrode polarized at a given potential. The potential was then shifted to the cathodic side, and a new spectrum with the same number of scans was assembled. The reference electrode used in this experiment was an Ag I AgCl I saturated KCl electrode. The IR spectra are represented as AR/R in the normalized form, where AR=R-R(E ), and R and R(E ) are the reflected intensity measured at a desired potential and a base potential, respectively. 

The most simple pentaeene OTFT test structure used in many labs is based on a Si wafer piece covered with a thermal oxide. Here, the heavily doped Si wafer takes the role of the back gate electrode, and the Si02 takes the role of the gate dielectric. A pentacene thin film is deposited as the semiconducting layer. Source and drain electrodes are deposited either on the silicon oxide (bottom contact) or on top of the pentacene film (top contact). 

Microfabrication and micromachining techniques have also been used in the manufacture of electrochemical sensors. This includes po and pco sensors. Zhou et al [9] describe an amperometric CO2 sensor using microfabricated microelectrodes. In this development, silicon-based microfabrication techniques are used, including photolithographic reduction, chemical etching, and thin-film metallization. In Zhou s study, the working electrodes are in the shape of a microdisk, 10 pm in diameter, and are connected in parallel. In recent years, silicon-based microfabrication techniques have been applied to the development of microelectrochemical sensors for blood gases, i.e. P02. Pcoj and pH measurements. 

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