Ariel J. Ben-Sasson

Patterned electrode vertical field effect transistor fabricated using block copolymer nanotemplates

We report the design and implementation of a vertical organic field effect transistor which is compatible with standard device fabrication technology and is well described by a self consistent device model. The active semiconductor is a film of C60 molecules, and the device operation is based on the architecture of the nanopatterned source electrode. The relatively high resolution fabrication process and maintaining the low-cost and simplicity associated with organic electronics, necessitates unconventional fabrication techniques such as soft lithography. Block copolymer self-assembled nanotemplates enable the production of conductive, gridlike metal electrode. The devices reported here exhibit On/Off ratio of 104.

Patterned electrode vertical field effect transistor: Theory and experiment

We present a theoretical and experimental investigation of the recently reported new architecture of a patterned electrode vertical field effect transistor (PE-VFET). The investigation focuses on the role of the embedded source electrode architecture in the device behavior. Current-voltage characteristics was unraveled through the use of a self-consistent numerical simulation resulting in guidelines for the PE-VFET architecture regarding the On/Off current ratio, output current density, and apparent threshold voltage. Current modulation characteristics are obtained through the formation of virtual contacts at the PE nano-features (i.e., perforations) under gate bias, which lead to the formation of vertical channels under drain bias. As the vertical channel is formed the device characteristics change from contact-limited to space-charge-limited. The analytical model strength is shown with the parameter extraction procedure applied to a measured PE-VFET device fabricated using block copolymer lithography an...

Solution-processed ambipolar vertical organic field effect transistor

We report on a solution-processed ambipolar patterned-electrode vertical organic field effect transistor (PE-VOFET) based on the P(NDI2OD-T2) polymer. The Schottky barrier-based VOFET operation uniquely facilitates an ambipolar transport using a single anode-cathode-electrode and a single semiconductor material. Pin-hole free sub-100 nanometer channel length devices are obtained with no high resolution patterning owing to both the polymer’s smooth morphology and the underlining patterned-electrode’s flatness. The VOFET exhibits n-type on/off ratio >103, current density >50 [mAcm−2] under VDS = 5 V, as well as p-type operation. Prone to design and optimization, the ambipolar PE-VOFET is a promising platform for organic complementary circuit technology.

Low-Temperature Molecular Vapor Deposition of Ultrathin Metal Oxide Dielectric for Low-Voltage Vertical Organic Field Effect Transistors

We demonstrate a low-temperature layer-by-layer formation of a metal-oxide-only (AlOx) gate dielectric to attain low-voltage operation of a self-assembly based vertical organic field effect transistor (VOFET). The AlOx deposition method results in uniform films characterized by high quality dielectric properties. Pin-hole free ultrathin layers with thicknesses ranging between 1.2 and 24 nm feature bulk dielectric permittivity, εAlOx, of 8.2, high breakdownfield (>8 MV cm(-1)), low leakage currents (<10(-7) A cm(-2) at 3MV cm(-1)), and high capacitance (up to 1 μF cm(-2)). We show the benefits of the tunable surface properties of the oxide-only dielectric utilized here, in facilitating the subsequent nanostructuring steps required to realize the VOFET patterned source electrode. Optimal wetting properties enable the directional block-copolymer based self-assembly patterning, as well as the formation of robust and continuous ultrathin metallic films. Supported by computer modeling, the vertical architecture and the methods demonstrated here offer a simple, low-cost, and free of expensive lithography route for the realization of low-voltage (VGS/DS≤3 V), low-power, and potentially high-frequency large-area electronics.

Fast switching characteristics in vertical organic field effect transistors

We report a theoretical and experimental investigation of the switching characteristics in patterned-source vertical field effect transistors. Experimentally we show that the layered structure gives rise to capacitances coupling of the potential between the drain and source electrodes. By removing the extrinsic gate-source capacitance we are able to demonstrate unprecedented sub-2 μs switching and current levels of 3 A/cm2. Theoretically, using a 2D drift-diffusion model, we show that the intrinsic response depends on two processes: the formation of the virtual electrode and the injection through it to form the vertical channel. The importance of the source structure parameter to achieve ultimate speed is discussed.