Macro Electronics
Research Activities
- Establishing Infrastructure for the Macro Electronics Project. In FY 2006, the Macro Electronics Project was established and integrated the joint MSEL/EEEL/CSTL Organic Electronics Competence (started FY 2005, originally under the Nanoelectronic Device Metrology Project). There are two areas of infrastructure that have been improved: personnel and equipment. Specifically, one full-time researcher joined NIST and the Macro Electronics Project, and the infrastructure needed to reproducibly fabricate organic devices with state-of-the-art performance and characterize the temperature dependence of their electronic properties was established.
- Joint NIST/Penn State U./U.
- Through this collaboration we have fabricated solution processed OTFTs with state-of-the-art performance in our laboratory. The soluble small-molecule organic semiconductor materials synthesized by the U. Kentucky Group have strong crystal forming properties, even when deposited by spin casting. Modifying the surface energy of the silicon dioxide gate dielectric and the source/drain contacts using molecules that form a self-assemble monolayer was found to strongly influence the film forming properties. For certain process conditions, highly ordered regions (large grains) were found to form along the contact edges and extend 10’s of micrometers into the channel region of the device. The temperature dependence of the extracted extrinsic field-effect mobility and the film microstructure in the channel were strongly correlated.
- Numerical Simulations of Design and Contact Related Effects for Organic Thin Film Transistors. Field-effect mobility for OTFTs is most often extracted for devices biased in the saturation regime. Plotting the square-root of the drain current as a function of the gate voltage yields a straight line for a well-behaved square-law device (ideal FET). It is from the slope of a line fitted to the linear part of this curve that the field-effect mobility is calculated. The threshold voltage is given by intercept. Using the 2-dimension drift diffusion program PISCES 2B numerical simulations were made for organic devices employing the NIST OTFT E-test structure and source and drain contacts with different work functions (WFs). For an organic semiconductor with a valance band edge located 5 eV below the vacuum level, a contact with a work function smaller than 4.8 eV causes a significant deviation from ideal square-law behavior; preventing the determination of values for field-effect mobility and threshold voltage which reflect the intrinsic properties of the organic semiconductor.
- Personnel. Since the project was formed in 2006, one full-time researcher has joined NIST and the Macro Electronics Project. Dr. David J. Gundlach (Penn State U.) was hired as the project leader after working on organic light emitting devices as a post-doctoral candidate at IBM Research Laboratory in
