Cornelis Maria Hart

Plastic transistors in active-matrix displays

The main advantages of using soluble semiconductive polymers in microelectronic devices are ease of processing and mechanical flexibility. Here we describe an active-matrix display with 64 × 64 pixels, each driven by a thin-film transistor with a solution-processed polymer semiconductor. In a significant step towards low-cost flexible displays, this polymer-dispersed liquid-crystal arrangement gives a reflective, low-power display with paper-like contrast, which can handle 256 grey levels while being refreshed at video speed.

Logic Gates Made from Polymer Transistors and Their Use in Ring Oscillators

Metal-insulator-semiconductor field-effect transistors have been fabricated from polymer semiconductors that can be processed from solution. The performance of these transistors is sufficient to allow the construction of simple logic gates that display voltage amplification. Successful coupling of these gates into ring oscillators demonstrates that these logic gates can switch subsequent gates and perform logic operations. The ability to perform logic operations is an essential requirement for the use of polymer-based transistors in low-cost low-end data storage applications.

Organic field-effect transistors and all-polymer integrated circuits

Electrical properties of field-effect transistors made of different solution processable organic semiconductors are described. The temperature and gate-voltage dependence of the mobility is shown and theoretically described using a model based on the variable-range hopping of charge carriers in an exponential density of states. Furthermore, a technology has been developed to make all-polymer integrated circuits. It involves reproducible fabrication of field-effect transistors on flexible substrates, where the semiconducting, conducting and insulating parts are all made of polymers. Integrated circuits consisting of more than 300 field-effect transistors are demonstrated.

Frequency behavior and the Mott–Schottky analysis in poly(3-hexyl thiophene) metal–insulator–semiconductor diodes

Metal–insulator–semiconductor diodes with poly(3-hexyl thiophene) as the semiconductor were characterized with impedance spectroscopy as a function of bias, frequency, and temperature. We show that the standard Mott–Schottky analysis gives unrealistic values for the dopant density in the semiconductor. From modeling of the data, we find that this is caused by the relaxation time of the semiconductor, which increases rapidly with decreasing temperature due to the thermally activated conductivity of the poly(3-hexyl thiophene).

Circuit yield of organic integrated electronics

Research on organic electronics is focussed on materials and on the performance of discrete devices. Reliability and circuit yield is largely unexplored. Yield, based on measurements on digital organic circuits up to 1000 transistors, is described. The causes of yield loss are analyzed and design solutions to improve the yield are discussed.

Polymeric integrated circuits and light-emitting diodes

All-polymer flexible integrated circuits have been fabricated using a potentially low-cost technology. Combination with commodity anti-theft stickers has led to functional radio frequent identification transponders. Polymeric light-emitting diodes (PLEDs) opened the way to cost efficient, large area display-applications. Directions for further enhancement of their performance are presented.

Low-cost all-polymer integrated circuits

A technology has been developed to make all-polymer integrated circuits. It involves reproducible fabrication of field-effect transistors in which the semiconducting, conducting and insulating parts are all made of polymers. The fabrication on flexible substrates uses spin-coating of electrically active precursors and patternwise exposure of the deposited films. In the whole process stack-integrity is maintained. Vertical interconnects are made mechanically. As a demonstrator for the technology functional 15-bit programmable code generators are fabricated. These circuits still operate when the foils are sharply bent. Due to the limited number of process steps the technology is potentially inexpensive.