Investigation of effects of polymer semiconductor blends on threshold voltage tuning of field effect transistors

• Main Author: Tan, Zhen Hao.
• Other Authors: Subodh Gautam Mhaisalkar
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/15438
• Institution: Nanyang Technological University

In this project, inverters were fabricated using three different thiophenes (P3HT, PQT and PBTDT) as the semiconductor layer and were electrically tested. All three polymer based inverters showed good switching characteristics and gain of > 2. However, due to the positive threshold voltage, the switching voltage shifted to more positive which is larger than the VDD, which then rendered its useless in organic circuit due to unmatching VIN to VOUT. Hence, for inverters to be functionable, threshold voltage control is essential. The project then moved into fabricating OFETs using different weight composition of polymer blends, to investigate the effect on tuning threshold voltage. In the second part of the project, a trend of threshold voltage shift was observed with mixing of thiophenes with different ionization energy (P3HT, PQT and PBTDT). The polymers were solution deposited by spin coating on silicon substrates with a double dielectric layer (silicon nitride and sol gel silica). Electrical characterization showed good mobilites, high on/off current ratios and good control of threshold voltage. Pure P3HT has positive threshold voltage of 5.71V and with addition of PQT and PBTDT, the threshold voltage shifted to the negative region. This method eliminates the extra fabrication step used to modify the dielectric interface which proves to tune the threshold voltage effectively.