Fredericus J. Touwslager

All-polymer ferroelectric transistors

We demonstrate thin-film ferroelectric transistors, made entirely from organic materials that are processed from solution. The devices consist of thin ferroelectric poly(vinylidene fluoride/trifluoroethylene) films sandwiched between electrodes made of conducting poly(3,4-ethylenedioxythiophene) stabilized with polystyrene-4-sulphonic acid. On top of this stack, an organic semiconductor is applied. The ferroelectric transistors, constructed using unipolar p- or n-type semiconductor channels, have remnant current modulations of ∼103 with a retention time of hours. They can be switched in 0.1–1ms at operating voltages less than 10V.

I-line lithography of poly-(3,4-ethylenedioxythiophene) electrodes and application in all-polymer integrated circuits

Industrialization of polymer electronics requires the use of safe solvents. To that end an I-line lithography process for conducting thin poly(3,4-ethylenedioxythiophene) films has been developed. The fully waterborne process is based on photocrosslinking using bisazide- and polyazide-type photoinitiators. The minimum feature size realized comprises 2.5 μm wide lines separated by 1 μm spacings. The sheet resistance is 1 kΩ/square. The process has been applied to fabricate all-polymer integrated circuits. The technology is demonstrated with functional 15-bit code generators.

Monitoring of polymerization-induced phase separation by simultaneous photo-d.s.c./turbidity measurements

Abstract Polymer—dispersed liquid crystals (PDLCs) can be used in displays. They can be made by polymerization-induced phase separation in a mixture of monomer and LC. Modification of a photo-d.s.c. with a laser and a photodiode enables the simultaneous measurement of heat flux and turbidity during polymerization. The heat flux yields the rate and conversion of the polymerization process, whereas turbidity indicates the appearance of a nematic phase. In this way the influence of the LC structure and content, the rate and temperature of polymerization and the cross-linker concentration on the phase separation process have been established for a simple model system. Recording of transmission—temperature curves before and after polymerization reveals the position of cloud points or clearing points in the phase diagram. The use of special cells allows the measurement of transmission—voltage curves on the d.s.c. samples after polymerization. The morphology, which is important with respect to electro-optical performance, strongly depends on the cross-link density at phase separation. Secondary phase separation inside LC domains already separated by cooling has been observed with microscopy during fast polymerization, not during slow reaction.

Water based I-line projection lithography of PEDOT

Structured conducting thin layers of poly(3,4-ethylenedioxythiophene) (PEDOT) have been made by photosensitizing a PEDOT latex which is stabilized with polystyrene sulphonic acid (PSS). The process is based on waterborne solutions only and makes use of negatively acting, highly sensitive, lithography with UV light of 365 nm (I-line). The minimum feature size obtained is 1 μm spacings and 2.5 μm lines with a sheet resistance of about 1 kOhm/square. The environmentally acceptable technology has been demonstrated with functional all-polymer integrated circuits prepared on 150-mm wafers.