MIM devices

Recently a novel experimental approach using Schottky diodes with ultra-thin metal films (see Fig. 11) makes direct measurement of reaction-induced hot electrons and holes possible. See for example Refs. 64 and 65. The chemical reaction creates hot charge carriers which travel ballistically from the metal film towards the Schottky interface and are detected as a chemicurrent in the diode. By now, such currents have been observed during adsorption of atomic hydrogen and deuterium on Ag, Cu and Fe surfaces as well as chemisorption of atomic and molecular oxygen, of NO and N02 molecules and of certain hydrocarbons on Ag. Similar results have been found with metal-insulator-metal (MIM) devices, which also show chemi-currents for many exothermic surface reactions.64-68... 

More recently, emission of light by a metal-CP-metal sandwich has been observed [235]. This is again a thin-film device, analogous to conventional MIM devices [230]. To some extent, such a light-emitting diode (LED) can be considered as the reciprocal of a photovoltaic cell. In the latter, absorption of a photon creates an electron-hole pair that is collected in the external circuit, whereas in the former, recombination of an electron and a hole that have been injected from the electrodes generates an emitted photon. LEDs using CPs are discussed in Section V.C. 

The selectivity of charge injection/extraction into/from the molecular HOMO or LUMO levels ensures the rectifying diode behavior of these organic devices [64]. The different working regimes of these MIM devices due to externally applied voltages are shown in Fig. 6. 

In this way a steady-state current was recorded upon exposing a Au film to a flux of H atoms that continuously recombine to H2 at the surface. A probability of 2 x 10 e/H atom was determined that is about two orders of magnitude smaller than that reported in Ref. [19], which has to be attributed to the higher energy barrier of the MIM device. 

The essential principle of an active matrix display is that each pixel has associated with it a semiconductor device that is used to control the operation of that pixel. It is this rectangular array of semiconductor devices (the active matrix) that is addressed by the drive circuitry. The devices, which are fabricated by thin-film techniques on the inner surface of a substrate (usually glass) forming one wall of the LCD cell, may be either two-terminal devices (Fig. 6) or three terminal devices (Fig. 7). Various two-terminal devices have been proposed ZnO varistors, MIM devices, and several structures involving one or more a-Si diodes. Much of the research effort, however, has concentrated on the three-terminal devices, namely thin-film, insulated-gate, field-effect transistors. The subject of thin-film transistors (TFTs) is considered elsewhere in this volume suffice it to say that of the various materials that have been suggested for the semiconductor, only a-Si and poly-Si appear to have serious prospects of commercial exploitation. 

Active-Matrix LCDs. Increase in FPD size along with demand for video response equivalent to the CRT made it necessary to avoid the high level of cross talk between adjacent pixels in passive displays. The nonlinear response of the liquid crystals was no longer suffieient and it became apparent that a switch was needed at each pixel. In principle, several switching technologies could be utilized since they all could be fabricated with films and photolithography. Metal-insulator-metal (MIM) devices, diodes, and transistors have all been tried. Thin-fihn transistors (TFTs) have performed the best and as a result have been adopted for most active-matrix applications. 

Studies of capacitance-voltage characteristics were done on metal insulator semiconductor (MIS) structures. The MIS structure consists of PCBM spin-coated on top of DNA-CTMA. For the metal electrode in the MIS device Cr/Au was chosen as the bottom as well as top electrode. Similarly, MIM devices were also fabricated and studied. For the MIM devices characteristics of capacitance vs frequency show no significant change in capacitance throughout the measured frequency range (see Fig. 21). On the other hand, MIS devices show rise in capacitance between frequency ranges of 10 to 10 Hz, corresponding to the dielectric relaxation of the PCBM semiconductor. At lower frequencies, capacitance further increases to an... 

An MJ can be considered a modified electrode with the solution replaced by a conductor, as shown in Figure 7.8b. This case is the classical metal/insulator/metal (MIM) device that was first treated theoretically in the 1960s to describe tunneling in metal or silicon oxides. A redox reaction need not be involved, and the observed current follows the empirical relationship of Equation 7.2. The absence of a redox reaction... 

Polyimides are known as good insulators with high thermal stability for microelectronics. Ultrathin films of polyimides were obtained by the LB technique [306,307]. The film was almost pin-hole free with a smooth surface [308] and the conduction mechanism in MIM (metal-insulator-metal) configuration was examined [309]. An electrical memory switching phenomenon was also observed in polyimide LB film incorporated in MIM devices [310]. 

A MIM device structure was constructed on a silicon wafer using arachidic acid and a C16TCNQ hetero-LB... 

Figure 14.45. Schematic view of a MIM device exhibiting an ultralow resistivity. (Reproduced by permission of The Japanese Journal of Applied Physics from ref 346.)...

The simplest and most widely used model to explain the response of organic photovoltaic devices under illumination is a metal-insulaior-metal (MIM) tunnel diode [55] with asymmetrical work-function metal electrodes (see Fig. 15-10). In forward bias, holes from the high work-function metal and electrons from the low work-function metal are injected into the organic semiconductor thin film. Because of the asymmetry of the work-functions for the two different metals, forward bias currents are orders of magnitude larger than reverse bias currents at low voltages. The expansion of the current transport model described above to a carrier generation term was not taken into account until now. 

MIM or SIM [82-84] diodes to the PPV/A1 interface provides a good qualitative understanding of the device operation in terms of Schottky diodes for high impurity densities (typically 2> 1017 cm-3) and rigid band diodes for low impurity densities (typically<1017 cm-3). Figure 15-14a and b schematically show the two models for the different impurity concentrations. However, these models do not allow a quantitative description of the open circuit voltage or the spectral resolved photocurrent spectrum. The transport properties of single-layer polymer diodes with asymmetric metal electrodes are well described by the double-carrier current flow equation (Eq. (15.4)) where the holes show a field dependent mobility and the electrons of the holes show a temperature-dependent trap distribution. 

The use of membrane introduction mass spectrometry (MIMS) was first reported in 1963 by Hoch and Kok for measuring oxygen and carbon dioxide in the kinetic studies of photosynthesis [46], The membrane module used in this work was a flat membrane fitted on the tip of a probe and was operated in the MIS mode. The permeated anaytes were drawn by the vacuum in the MS through a long transfer line. Similar devices were later used for the analysis of organic compounds in blood [47], Memory effects and poor reproducibility plagued these earlier systems. In 1974, the use of hollow-fiber membranes in MIMS was reported, which was also operated in the MIS mode [48], Lower detection limits were achieved thanks to the larger surface area provided by hollow fibers. However, memory effects caused by analyte condensation on the wall of the vacuum transfer line remained a problem. 

Fig. 5.1. Charge generation process in a single-layer conjugated polymer device under short-circuit conditions in the MIM model. VB valence band, CB conduction band, Eg bandgap, P+, P positive and negative polarons...

The experimentally observed Voc of PSC cannot be explained by the MIM picture alone. For typical devices, based on ITO/conjugated polymer fullerene/Al, values of Voc can be observed in a range of 800 mV and higher for several polymer/fullerene mixtures, in contrast to the 400 mV expected from the MIM picture. The origin of the open-circuit voltage in plastic solar cells will be discussed and explained in Sect. 5.3.4. 

First, the drift current is calculated in the case of a constant electrical field, as one would expect for very thin bulk heterojunction solar cells. If the width W of the active layer is similar to the drift length of the carrier, the device will behave as a MIM junction, where the intrinsic semiconductor is fully depleted. The current is then determined by integrating the generation rate G = —dP/dx over the active layer, where P is the photon flux ... 

Mihailetchi [134] investigated the open circuit voltage of the bulk heterojunction organic solar cells based on methanol-fullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as electron acceptor and poly[2-methoxy-5(3 ,7 -dimethyloctyloxy)-p-phenylene vinylene] (OC1C10-PPV) as an electron donor. It is known that a single layer device follows the MIM model [166] and the open circuit voltage V0c is equal to the difference in the work functions of the metal electrodes [134], If charges accumulate in the... 

To confirm the MIM structure can excite radiative SPPs, we have simulated the transmission spectra of Al / Si02 / Al structure on fused silica substrate and the results for p-polarization are shown in Fig. 13.18. The total thickness of the Al layers is taken to be 50 nm. Al is chosen because it forms an Ohmic contact with ZnO so that it is advantageous for device fabrication [43]. 

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