Paul F. Baude

Pentacene-based radio-frequency identification circuitry

Pentacene-based thin-film integrated circuits patterned only with polymeric shadow masks and powered by near-field coupling at radio frequencies of 125 kHz and above 6 MHz have been demonstrated. Sufficient amplitude modulation of the rf field was obtained to externally detect a clock signal generated by the integrated circuit. The circuits operate without the use of a diode rectification stage. This demonstration provides the basis for more sophisticated low-cost rf transponder circuitry using organic semiconductors.

High Performance Organic Thin Film Transistors

We report here methods of surface modification and device construction which consistently result in lab-scale pentacene-based TFTs with mobilities at or above 5 cm 2 /Vs. Surface modifications include polymeric ultrathin films presenting a passivated interface on which the semiconductor can grow. High performance TFTs have been fabricated on a variety of dielectric materials, both organic and inorganic, and are currently being implemented in manufacturable constructions. Our surface modifications have also proven useful for substituted pentacene materials and for a variety of other organic semiconductors. In addition, we report an all organic active layer, rf-powered integrated circuit. Further experiments and statistical analyses are underway to explain the elevated mobility in our samples, and efforts have been made to confirm these results through collaboration.

Fabrication of sol‐gel derived ferroelectric Pb0.865La0.09Zr0.65Ti0.35O3 optical waveguides

Crack‐free transparent ferroelectric Pb0.865La0.09Zr0.65Ti0.35O3 [PLZT (9/65/35)] thin films have been deposited on silicon substrates using the sol‐gel deposition technique. An intermediate layer of Pb0.90La0.10Ti0.975O3 (PLT) was used to improve the PLZT’s optical quality and to reduce the amount of film cracking. Wet chemical etching, plasma etching, and reactive ion etching were investigated as means of realizing the necessary waveguide structures. Waveguiding was observed in 2–4 mm long by 20 μm wide PLZT (9/65/35) ridge waveguides fabricated by reactive ion beam etching.

Deep level transient spectroscopy characterization of ferroelectric Pb(Zr,Ti)O3 thin films

Deep level transient spectroscopy (DLTS) has been used to investigate trap levels in sol‐gel derived polycrystalline Pb(Zr0.54,Ti0.46)O3 thin films. Metal‐ferroelectric‐metal capacitor structures 2400 and 3000 A in thickness were fabricated and characterized using a constant voltage DLTS system. Prominent peaks associated with a single trap level were observed in all samples studied. The activation energy was determined to be 267 meV from DLTS spectra Arrhenius plots. Infrared transmission characterization was performed on PbTiO3 thin films also prepared using sol‐gel synthesis. A loss in the transmission at 270±12 meV was observed which we attribute to hole emission from the same trap detected using DLTS.

Polymeric aperture masks for high performance organic integrated circuits

The use of polymeric aperture masks to fabricate high performance pentacene-based integrated circuits is presented. The aperture masks are fabricated using a laser ablation process with capabilities of generating 10 μm features. A mask set consisting of 4–6 aligned layers has been fabricated and has been used to demonstrate functional rf-powered integrated circuits with 20 μm gate lengths. Devices consisted of shadow-mask patterned layers of gold, alumina, and pentacene. TFT mobilities greater than 2 cm2/V s were measured and propagation delays from 7-stage ring oscillators of less than 5 μs were observed. This all-additive, dry patterning method has been extended to the production of samples as large as 6 in.×6 in. Larger aperture masks are under investigation and continuing efforts are focused on automation of the alignment process.

Critical phenomena and phase transition in SOL-GEL derived ferroelectric PLZT thin films

Abstract Lanthanum doped Pb(Zr, Ti)O3 thin films have been fabricated by the solgel deposition technique. The small-signal dielectric constant ϵ has been investigated in the temperature range of 25°C to 550°C. The maximum value in the dielectric constant occurs at certain temperature for each particular composition. The apparent critical temperature is close to the Curie temperature reported in literature for the bulk material with similar composition. Lanthanum modified PbTiO3 and PbZrTiO3 have shown lower and broaden peaks. Ferroelectric hysteresis loops have been observed. The shape of the loop, the amplitude of the remnant polarization, and the coercive field significantly changed when the films were heated across the critical temperature that appeared in the dielectric constant curve. The critical temperature is assumed to be associated to the phase boundaries between the paraelectric-cubic and the ferroelectric tetragonal phases. A diffuse phase transition region were observed in lanthanum doped films.

Micromachined infrared detectors based on pyroelectric thin films

Solid-state micromachining techniques have been used in the fabrication of low-stress silicon nitride thermal isolation structures for pyroelectric detectors. Thin films of PbTiO(subscript 3/ and other related Perovskite materials are integrated on these structures. Process compatibility with NMOS electronics is demonstrated.

Characterization of sol-gel derived (Pb,Ba)(Zr,Ti,Nb)O3 thin films for optical waveguide development

(PbBa)(ZrTiNb)0 3 thin films and powders have been prepared using the sol-gel technique. Solutions were synthesized in 2-methoxyethanol based upon our previous PZT solution preparation. Three different approaches were used for incorporating barium into PZT alkoxide solutions. Thermal analysis and x-ray diffraction results indicated that barium methoxypropoxide gave the best results. PBZTN (71% Pb and 71% Zr) was deposited onto sapphire substrates as well as oxidized silicon substrates. Optical transmission measurements showed greater than 80% transmission for wavelengths longer than 400 nm. Films with thickness of 3000 A on sapphire exhibited a refractive index of 2.19 at λ=633 nm.

39.2: Invited Paper: Large area, High Performance OTFT Arrays

Recent efforts at 3M have extended the use of polymeric aperture masks and surface modification methods to produce large area (approximately 6″×6″) arrays of high mobility pentacene TFTs on a variety of substrates. Results of high performance organic TFTs in active matrix display backplanes will be presented.