Electrically Stable Organic Permeable Base Transistors for Display Applications

Abstract

Unfortunately, high-resolution patterning techniques operating in the nanometer regime are costly and currently incompatible with the promise of low-cost flexible electronics. Hence, new device concepts need to be conceived which allow for an ultra-short channel length in conjunction with low fabrication costs. In this regard, vertical organic transistors with a channel length of ≈100 nm have generated significant interest in recent years, [4][5][6][7][8][9][10] as the vertical dimensions of an organic transistor can be easily controlled over the nanometer regime. The organic permeable base transistor (OPBT) is a truly vertical device with a semiconductor thickness in the order of 100 nm. Due to the extraordinarily short channel and a reduced influence of the contact resistance, [11] the OPBT can drive very large current densities above 1 kA cm −2[12] and reaches record-high transition frequencies of 40 MHz, [3] making it the fastest organic transistor to date. The transistor consists of a vertical stack of three electrodes separated by organic semiconductor layers. The outer electrodes constitute emitter and collector, while the central electrode is the base. It has native nano-sized holes, making it permeable for electrons. Current leakage into the base is prevented by a native oxide film around the electrode. In the on-state, a charge-accumulation channel at the oxide interface is formed, ensuring efficient charge transport through the base, while in the off-state the base potential hinders the charge conduction through the pinholes. Figure 1 shows a cross-sectional transmission electron microscopy (TEM) image of an OPBT with C 60 semiconductor layers and the ultra-thin permeable base electrode of aluminum.These advances enable a broad range of possible applications for OPBTs, including display driver circuits where high currents and fast switching are needed, [13] and radio-frequency identification (RFID) systems with MHz operation. [14,15] Realworld applications, however, require a number of other properties like integrateablity, low power consumption, and stability. OPBTs operate on low voltages, generally enabling facile integration into electronic circuits. The static power consumption of OPBTs was recently dramatically reduced by the introduction of a controlled base oxidation technique. [16] Stability, though, has not yet been studied for OPBTs and there is little research regarding the behavior of short-channel vertical organic transistors under continued electrical stress.Vertical organic permeable base transistors (OPBT) can drive large current densities of kA cm −2 and achieve record-high transition frequencies of up to 40 MHz. They are therefore an interesting candidate for numerous applications, including the use in active-matrix organic light emitting display (AMOLED) backplanes. However, the transistor characteristics are required to be stable against electrical stress. Here, the threshold voltage shifts under current-and voltage-stress conditions over various temperatures and illumination condi...

A Review of Vertical Organic Transistors

“…Later the focus shifted to p‐type OPBTs, where a similar level of performance had been reached . The real performance breakthrough though came with Fischer et al who reported in a series of papers on the continuous improvement of an n‐type OPBT, which ultimately led to the performance records mentioned previously. Furthermore, Fischer and co‐workers also developed a detailed theory on the device operation, which is used here for the discussion of the OPBT operation.…”

“…The huge potential for OPBTs to be used in high‐power and high‐frequency applications has very recently been underlined by Dollinger et al reporting for the first time on the electrical stability of OPBTs under high‐power stress conditions. In this publication, Dollinger judged on the device stability by means of the threshold voltage shift Δ V th which has been measured under continuous off‐state stress (electric field stress at 0.1 MV cm −1 ), but most importantly also under continuous on‐current stress at a high current density of 3 A cm −2 .…”

“…The stress effect scales linearly with the applied current. Reproduced with permission . Copyright 2019, Wiley‐VCH.…”

Organic Complementary Inverters Based on Vertical-Channel Dual-Base Thin-Film Transistors with Time Constants < 10ns

“…One vertical organic transistor structure that stands out of all proposed approaches is the organic permeable base transistor (OPBT) which is the organic transistor with the highest transition frequency reported 29 . Furthermore, OPBTs show excellent stability comparable to the best lateral OTFTs 30 . However, complementary inverter circuits based on vertical organic transistors have not been reported so far which is mainly caused by the lack of proper p-or n-type transistors.…”

High‐Performance Static Induction Transistors Based on Small‐Molecule Organic Semiconductors

“…These devices offer very short channels compared to their planar counterparts because the thickness of a semiconductor layer can range from a few nanometers to several hundred nanometers. [ 11–16 ]…”