Spin-on Polymer Gate Dielectric for High Performance Organic Thin Film Transistors
- PDF / 1,630,552 Bytes
- 6 Pages / 390.24 x 621.36 pts Page_size
- 22 Downloads / 186 Views
ABSTRACT We have investigated the polymeric insulators benzocyclobutene (BCB), parylene C and polyimide for use as gate dielectrics in pentacene organic thin film transistors (TFTs). Atomic force microscopy (AFM) was used to examine the surface roughness of the polymeric dielectrics and the morphology of pentacene films deposited onto them. X-ray diffraction was used to examine the molecular ordering of pentacene films deposited onto the polymeric dielectrics. We find a correlation between the surface roughness of the gate dielectric and the grain size in deposited pentacene films, with smooth surfaces yielding larger, more dendritic grains. Despite significant changes in film morphology, pentacene TFTs using BCB, parylene C, or polyimide as the gate dielectric have performance comparable to devices using SiO 2 as the gate dielectric. These results suggest that there is not a strong correlation between pentacene film grain size and field-effect mobility for these devices. Pentacene TFTs using BCB as the gate dielectric had field-effect mobility as high as 0.7 cm 2/V-s, on/off ratio > 107, subthreshold slope less than 2 V/decade, and negative threshold voltage, making them an attractive candidate for use in organic-based large-area electronic applications on flexible substrates. INTRODUCTION Thin film transistors (TFTs) are widely used for large-area electronics applications such as flat panel displays. Organic semiconductors, which have low processing temperatures, may allow for low-cost TFTs on lightweight, flexible and inexpensive polymeric substrates. Potential applications are all-organic emissive displays, smart cards, smart inventory tags, and large-area sensor arrays. TFTs based on the small-molecule organic semiconductor pentacene have demonstrated device performance comparable to a-Si:H TFTs (tlFE > 1.0 cm 2/V-s, on/off current ratio > 107, subthreshold slope < 2 V/decade) [1]. A low-cost organic dielectric that can be deposited easily at low temperature would be of interest for organic circuits and devices on polymeric substrates EXPERIMENTAL Material Characterization Three polymeric insulating materials were chosen for investigation as pentacene TFT gate dielectrics: benzocyclobutene (BCB), parylene C, and a thermally imidized polyimide. The desired properties of organic gate dielectrics include good solvent resistance for compatibility with photolithographic processing, high dielectric strength, high resistivity, low processing temperature for compatibility with polymeric substrates, a simple low-cost deposition process, and small surface roughness. BCB was obtained from Dow Chemical Company under the trade name Cyclotene® 3022. BCB has been investigated extensively as a dielectric in thin film multichip modules [3], as an interlevel dielectric in integrated circuits [4], and as a planarization 403
Mat. Res. Soc. Symp. Proc. Vol. 558 02000 Materials Research Society
layer in a-Si:H TFTs for AMLCDs [5] due to the material's excellent planarization properties. The precursor required for the vacuum depo
Data Loading...
