Ph.D Thesis

Ph.D StudentGreenman Michael
SubjectUnderstanding and Controlling Vertical Organic Field
Effect Transistor for Basic Applications
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROF. Nir Tessler


The organic transistor is a thin film transistor based on a carbon-hydrogen compounds (organic) semiconductor. Thanks to the simple deposition techniques of organic semiconductors, the organic transistor is a candidate for switching elements in wearable and other low-cost electronics. Unlike the organic LEDs, the organic transistor has not reached, yet, the performance needed by the industry. The organic semiconductors’ low mobilities (0.1 cm2/Vs) are hindering the device current density and frequency response. Vertical organic field effect transistor (VOFET) is one approach to overcome the organic semiconductors’ low mobilities. In vertical transistors, the channel length is the semiconductor film thickness, thus it is possible to fabricate a short channel (~100nm) high-performance device while keeping the fabrication process relatively low-cost and large-area compatible.

In this work, a structure and fabrication methods for VOFET called patterned source electrode (PSE) was studied by fabricating and characterizing different structures of the VOFETs. In the PSE-VOFET, the gate electrode is located beneath the source electrode and controls the number of carriers injected from the source electrode to the organic semiconductor. From the semiconductor, the carriers swiftly cross the very short channel length towards the drain electrode. Using exotic block copolymer self-assembly technique, fast (~1 µsec) and high current density (3 A/cm2) VOFETs were fabricated. To obtain more robust process, photolithography was used to fabricate N-type and P-type PSE-VOFETs with a source insulator layer. The source insulator layer improves the high on/off ratio (>105). Those PSE-VOFETs were successfully assembled to complementary inverter circuits and light emitting transistors. Reaching drain saturation regime is not trivial in VOFETs and most of them lacking the saturation needed to drive OLEDs in active matrix displays. By improving the fabrication process, a saturation regime was also achieved.