Vertical organic transistors

Abstract

A capacitor that basically consists of two parallel metal plates with dielectric materials in between, can store charge at the two inner surfaces of the metal plates when a voltage bias is applied. As the thickness of the metal-plate electrodes decrease to nanometers range, we find an interesting physical phenomenon, i.e., the stored charges can modify the physical properties of the semiconductor layer coated on top of it. This discovery leads us to demonstrate a whole-new concept field-effect transistor, a vertical organic transistor with a novel device structure by stacking gate-source-drain vertically. This vertical stack consists of an active cell (drain/organics/source) on top of a capacitor cell (source/dielectrics/gate). When the gate (capacitor) is biased, charges are stored in the capacitor cell. As the thickness of the source electrode is thin enough, typically in the nanometer range, the active cell can also sense the stored charges within the capacitor cell, and, subsequently, modulate the charge injection from the source into the organics. This unique device structure provides an extremely short length and large channel conduction area. As a result, we achieved organic transistors with low working voltage (less than 5 V), high current output (up to 10 mA or 4 A/cm 2 ), and high ON/OFF ratio (up to 4×10 6 ). This device solves two long-standing issues with organic transistors, high working voltages and low current output. This novel device with its enhanced operating characteristics opens new directions for organic transistors and their applications. The device operation mechanism is different from traditional field effect transistors, where we proposed an injection-controlled mechanism, which can basically explain the observed electrical phenomenon of our vertical transistors.