Preparation of Thin Film Devices

Thin film opto-electronic devices, such as LEDs, modulators and photocells all require the deposition of one or more thin semiconductor layers onto a substrate. Such films are usually of thickness in the range between 50 nm and 10/xm. 

Thin films of organic semiconductors have been deposited onto substrates either from solution or from the vapor phase. The method of choice depends mainly on the molecular weight and solubility of the material. 

In order to transfer the attractive solution-processing properties of polymers to oligomers, the smaller oligomers can be rendered soluble either by suitable chemical modifications, such as addition of alkyl side-chains in a similar fashion as the poly(3-alkylthiophenes) [34-37] (see Fig. 2b,c) or else they can be blended within a soluble polymer [10-12, 14, 15] or chemically grafted as pendant side-chains on a polymer backbone [16, 17], as shown in Fig. 3. 

---

Although polymerization of NIPAAm has been extensively investigated in the past using free radical initiator, this method can not be used for the preparation of thin films. Thin hydrogels films can find applications as microfluidic devices for sensors and actuators in case patterning is possible. This problem can be solved by preparing gel films from narrowly distributed microgel particles (Zhou and Wu... 

The Langmuir-Blodgett(LB) technique allows the preparation of thin films with a defined number of monolayers. This is of special importance for the development of molecular electronic devices based on ordered superstructures of the grids with an exactly defined film thickness. 

To check an electroactivity of catalysts, cyclic voltammetry method for a three-electrode cell system was performed. We had prepared a working electrode by coating the catalyst powder mixed with Nafion polymer onto a glassy carbon electrode. The preparation of thin film electrodes followed the previous researchers method [74-76]. Electrochemical impedance spectroscopy (EIS) measurements were studied by means of above electrochemical device coupled with FRA2 module (Eco Chemie, Netherlands) in a frequency range of 1 MHz - 0.1 Hz. 

The successful development of these thin films for device applications requires that two goals be met (1) the preparation of materials with device quality characteristics and (2) for certain applications, successful integration of the thin film with underlying silicon circuitry, without degradation of circuitry performance characteristics. A number of analytical characterization techniques have been employed to study film preparation and thin film—device integration issues. Some of these techniques and their applicability in characterizing ferroelectric thin film device preparation will be briefly discussed. 

Preparation of thin films is an important step for semiconductors and related devices. These films can be prepared following some of the techniques described, such as CVD and its variants (PECVD, LEPVD, MOCVD, etc.). Some methods (e.g., sputtering, evaporation, and molecular beam epitaxy) have been mostly developed to prepare metal films or III-V semiconductors, and will not be discussed here. Other methods are more versatile and can be used to prepare metal oxide films. 

Polymers. The Tt-conjugated polymers used in semiconducting appHcations are usually insulating, with semiconducting or metallic properties induced by doping (see Flectrically conductive polymers). Most of the polymers of this type can be prepared by standard methods. The increasing use of polymers in devices in the last decade has led to a great deal of study to improve the processabiUty of thin films of commonly used polymers. 

Dendrimers have also been found useful in the construction of thin films containing isolated fullerenes [85, 86]. Such materials could eventually find practical application in sensors and/or optoelectronic devices [87]. Generally, monolayers prepared from C60 are ill-defined due to the aggregation tendency of fullerenes. The covalent attachement of C60 to bulky dendritic frameworks... 

Chien and Cada [42] have prepared optically active and photoactive SCLC copolymers, 15, with the 4-alkoxyphenyl-4 -alkoxycinnamate chromophore, with the intention of creating LC polysiloxane networks that could be used to prepare macroscopically oriented organic ferroelectric polymers for electro-optical devices. Optical activity was introduced into the polymer by the use of a chiral spacer. Those copolymers which were mesogenic exhibited properties characteristic of a Sc. phase. UV-irradiation of thin films of the polymers in their mesomorphic states at 90°C, led to a loss of the IR absorption at 1635 cm-1 that is due to the cinnamate double bond, and to cross-linking. Long-term irradiation led to... 

---