Annie Wang

Direct Monolithic Integration of Organic Photovoltaic Circuits on Unmodified Paper

There has been signifi cant recent interest in integrating electronics into low-cost paper substrates, including transistors, storage devices, displays, and circuitry. [ 1–4 ] Paper-based photovoltaics (PVs) could serve as an “on-chip” power source for these paper electronics, and also create attractive new paradigms for solar power distribution, including seamless integration into ubiquitous formats such as window shades, wall coverings, apparel, and documents. Module installation may be as simple as cutting paper to size with scissors or tearing it by hand and then stapling it to roof structures or gluing it onto walls. Moreover, paper is ∼ 1000 times less expensive ( ∼ 0.01

Tunable threshold voltage and flatband voltage in pentacene field effect transistors

· m − 2 ) than traditional glass substrates ( ∼ 10

Engineering density of semiconductor-dielectric interface states to modulate threshold voltage in OFETs

· m − 2 ) [ 5 , 6 ]

Process control of threshold voltage in organic FETs

Charged interface states are introduced by UV-ozone treatment of a polymer gate dielectric, parylene, prior to deposition of the organic semiconductor, pentacene, thereby modifying the organic field effect transistor (OFET) operation from enhancement to depletion mode. Quasistatic capacitance-voltage measurements and the corresponding current-voltage characteristics show that the threshold voltage VT and flatband voltage VFB can be shifted by over +50V, depending on the ozone exposure time. This work demonstrates that careful control of the semiconductor-insulator interface state densities is essential to VT and VFB control and the fabrication of reliable OFET integrated circuits.

Electrically tunable organic vertical-cavity surface-emitting laser

Threshold-voltage control is critical to the further development of pentacene organic field-effect transistors (OFETs). In this paper, we demonstrate that the threshold voltage can be tuned through chemical treatment of the gate dielectric layer. We show that oxygen plasma treatment of an organic polymer gate dielectric, parylene, introduces traps at the semiconductor-dielectric interface that strongly affect the OFET performance. Atomic force microscopy, optical microscopy using crossed-polarizers, and current-voltage and capacitance-voltage characterization were performed on treated and untreated devices. A model is presented to account for the effects of trap-introduced charges, both 1) fixed charges (2.0/spl times/10/sup -6/ C/cm/sup 2/) that shift the threshold voltage from -17 to +116 V and 2) mobile charges (1.1/spl times/10/sup -6/ C/cm/sup 2/) that increase the parasitic bulk conductivity. This technique offers a potential method of tuning threshold voltage at the process level.

Transfer-printed composite membranes for electrically-tunable organic optical microcavities

We report a technique for systematically modifying the threshold voltage of pentacene organic FETs at the process level. Threshold voltage control is critical to practical circuit design using OFETs, since it ultimately determines circuit functionality and yield. This work shows that oxygen plasma and UV-ozone treatments of an organic polymer gate dielectric, parylene, introduce traps at the semiconductor-dielectric interface. We model the effects of trap-introduced charges as both fixed charges that shift the threshold voltage and mobile charges that increase parasitic bulk conductivity. I-V and C-V characterization confirm that threshold voltage can be varied from - 27V to +26V by exposure to UV-ozone and from -17V to +116V by exposure to oxygen plasma. Optical measurements confirm the presence of a trap level at 420nm (3.0eV) in response to the treatment.

Printed MEMS membranes on silicon

An electrically tunable organic vertical-cavity surface-emitting laser (VCSEL) is demonstrated and characterized. A lasing wavelength tunability of Δλ = 10 nm with 6 V actuation is shown for a red laser emission tuned between λ = 637 nm and λ = 628 nm. Wavelength tuning of the VCSEL structure is enabled by electrostatic deflection of a reflective flexible membrane that is suspended over an air gap and a dielectric mirror, forming a 3λ lasing cavity. The lasing gain medium consists of an evaporated organic thin film coated on a reflective membrane, which is then additively placed over a patterned substrate containing the dielectric mirror to fabricate an array of air-gap-VCSEL structures, each 100 μm in diameter. Beyond the electrostatic actuation of these tunable lasers, the VCSEL array geometry also has the potential to be used as pressure sensors with an all-optical remote excitation and readout and a pressure sensitivity of 64 Pa/nm in the demonstrated configuration.

Electrically tunable organic vertical cavity surface emitting laser

We demonstrate a method for fabricating organic optical microcavities which can be electrostatically actuated to dynamically tune their optical output spectra. Fabrication of an integrated organic micro-opto-electro-mechanical system (MOEMS) cavity is enabled by the solvent-free additive transfer of a composite membrane. Electrical actuation and optical characterization of a completed cavity show resonance tuning greater than 20 nm for membrane deflections of over 200 nm at 50 V.

A Low Temperature Fully Lithographic Process For Metal–Oxide Field-Effect Transistors

We report a new method for additive fabrication of thin (125±15 nm thick) gold membranes on patterned silicon dioxide (SiO2) substrates for acoustic MEMS. The deflection of these membranes, suspended over cavities in a SiO2 dielectric layer atop a conducting electrode, can be used to produce sounds or monitor pressure. This process uses a novel technique of dissolving an underlying organic film using acetone to transfer membranes onto SiO2 substrates. The process avoids fabrication of MEMS diaphragms via wet or deep reactiveion etching, which in turn removes the need for etch-stops and wafer bonding. Membranes up to 0.78 mm2 in area are fabricated and their deflection is measured using optical interferometry. The membranes have a maximum deflection of about 150 nm across 28 μm diameter cavities. Youngs modulus of these films is shown to be 74±17 GPa, and their potential sound pressure generation at 15 V is calculated.

Molecular organic electronic circuits

Using solvent-free composite membrane transfer, we demonstrate an electrically tunable organic visible light-emitting laser with reversible tuning range of 10 nm under 6 V actuation. Large-area scalability of utilized fabrication methods suggests potential use in all-optical pressure-sensing surfaces.