Polymer Insulator Layers

We have attempted to use a variety of organic insulators which could be conveniently prepared for use in MIS structures. Most of the effort has been made with polyimide, which has the best dielectric strength of those we have used here nevertheless this is about an order of magnitude lower than that of Si02- Details of the methods used to deposit these materials are given in section 3.2. 

Poly(methylmethacrylate), PMMA, is soluble in the solvents used for the Durham polyacetylene precursor, so that deposition of the polyacetylene was made first, followed by the PMMA layer. Note that in this case, the insulator/semiconductor interface is made at the tq , free surface of the polyacetylene, and we can expect that there are differences in the structure of top and the bottom surfaces. We return to this later in connection with the electro-optical properties of the MIS devices in section 6.3. The variation of the differential capacitance with bias voltage for a MIS device built in this way is shown in figure 29. It shows a very similar form to that seen for the other MIS devices, and standard analysis of the capacitance in the depletion regime gives values of Na = 2.1 x 10 6 cm 3 and Vf = -1 V. 

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C. C. Shiflett, D. B. BuchhoF, and C. C. Faudskar, "High-Density Multilayer Hybrid Circuits Made with Polymer Insulating Layers (Polyhic s)," Society of Hybrid Microelectronics Proceedings, 1980, pp. 481—486. 

Polymer Insulating Layers for Multilayer Hybrid Circuits... 

How much do the results we have obtained here tell us about the fundamental limits to the mobilities of carriers in devices fabricated with polymer that is very much better ordered than the polyacetylene that we have used here There are recent reports of very much improved mobilities for devices based on sexithiophene (the six repeat unit oligomer of polythiophene), with a value of 0.4 cm /Vsec now reported [73], and there is now considerable interest in the development of polymer FETs as large area thin film transistors, with interest in polythiophene derivatives [74] and in poly(arylenevinylenes) such as poly(2,5-thienylene vinylene) [75]. We can see from the optical characterisations of the MIS devices that the surface layer of polyacetylene formed on SiC>2 is very much more disordered than the bulk material, but we have not made FET devices with the polymer insulator layers which give better ordered structures as characterised optically. 

A disadvantage of AES is that the intense electron beam easily causes damage to sensitive materials (polymers, insulators, adsorbate layers). Charging of insulating samples also causes serious problems. 

Protective Coatings. Some flame retardants function by forming a protective Hquid or char barrier. These minimize transpiration of polymer degradation products to the flame front and/or act as an insulating layer to reduce the heat transfer from the flame to the polymer. Phosphoms compounds that decompose to give phosphoric acid and intumescent systems are examples of this category (see Flame retardants, phosphorus flame retardants). 

A recent development of the insulated runner principle is the distribution tube system. This overcomes the possibility of freezing-off by insertion of heated tubes into the runners. However, this system still relies on a thick layer of polymer forming an insulation layer on the wall of the runner and so this system is not suitable for heat sensitive materials. 

Thus it has been shown that thin insulating layers (in the nanometer range) at the interface metal/polymer in a PLED can significantly reduce the onset electric field necessary for EL [58-63]. This is still not fully understood and has been ascribed to band bending at the interface [64]. 

A special problem can be the passivation of the electrode surface by insulating layers, for example, formation of oxides on metals at a too high anodic potential or precipitation of polymers in aprotic solvents from olefinic or aromatic compounds by anodic oxidation. As a result, the effective surface and the activity of the... 

It usually takes place close to the melting temperature of the polymer when the pores collapse turning the porous ionically conductive polymer film into a nonporous insulating layer between the electrodes. At this temperature there is a significant increase in cell impedance and passage of current through the cell is restricted. This prevents further electrochemical activity in the cell, thereby shutting the cell down before an explosion can occur. 

Microphase separated block copolymer systems derived from a high temperature polymer with a thermally unstable polymer that undergoes thermal decomposition at elevated temperature to leave pores In the Insulating layer. 

Detectors d are formed as mesa-structure pn-junctions on a substrate 3. An insulation layer 1 is formed by a polymer film or by a vacuum layer. The radiation applied to the array may come from the side of the substrate opposite to the side which carries the detectors, indicated by the wavy arrow 7. In this case, in order to ensure practically complete absorption of the radiation... 

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