Failure Modes of Organic Devices

• Main Author: Sessford, Joanna Ruth
• Published: University of Liverpool 2008
• Subjects: 621.3815
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502300

Research into Organic Electronics has increased dramatically over the past 20 years. Organic Electronics cannot compete with single crystal silicon for speed and circuit complexity, but it can be regarded as a competitor because of its potential to produce very large area circuits at low process temperatures and low cost. Potential applications for conjugated polymer devices include photovoltaic cells (low cost solar panel), optical amplifiers, memory, displays (in conjunction with e-paper and large area LCD's) and radio frequency (RFID). Many of these devices will use Thin Film Transistors (TFTs). TFT characteristics are therefore discussed with 'an emphasis on the hysteresis observed; the results observed indicate that one ofthe causes ofhysteresis is ion movement. A number of different current-voltage equations have been derived for the drain current channel. It is important to develop these equations to determine the effect of treating the real variation in the concentration of carriers, normal to the interface. In addition, how this large variation in the density of carriers gives rise to an enhancement of carrier mobility at the interface is approached, has been examined. It has been shown that for devices fabricated using PTAA; the most appropriate equation is that which assumes the exponential distribution of states depends on electron concentration. MOS capacitors are important test structures; they are useful because of the light they shed on electrical instability in organic devices, MOS capacitors characteristics have therefore been discussed before the hysteresis they display has been examined. The following mechanisms of hysteresis in MOS capacitors have been examined: carrier hopping, carrier percolation, gate leakage current, ion movement in the semiconductor and instability in the gate dielectric. The main causes of instability appear to be oxygen ions in the semiconductor and in the gate dielectric. The hysteresis observed in Schottky diodes has also been examined; contributing factors appear to include ion movement and diffusion. Values for Meyer Neldels energy for ; . Schottky diodes fabricated using Lisicon (undoped) have been calculated to be 5.0.10-21 ; this value increases when dopant is added; this is expected as doping introduces more states and at high levels of doping leads to Fermi level pinning. As Organic Electronics is growing rapidly into an industry, it is vital to have aroadmap; to allow equipment manufacturers and semiconductor technologists to plan targets for the future, this piece of work provides a roadmap for Organic Electronics. One of the major potential uses of Organic Electronics is believed to be in the area of auto hI/rf tags, for example, the replacement of the barcode, the roadmap therefore concentrates on this area; it has been predicted that by the year 2030 full barcode replacement will be available at an economic cost.