Operation mechanism of high performance organic permeable base transistors with an insulated and perforated base electrode

Kaschura, Felix; Fischer, Axel; Klinger, Markus P.; Doan, Duy Hai; Koprucki, Thomas; Glitzky, Annegret; Kasemann, Daniel; Widmer, Johannes; Leo, Karl

doi:10.1063/1.4962009

Cited by 22 publications

(41 citation statements)

References 22 publications

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“…[22] It can thus be assumed that any effects of on-stress predominantly occur in the base electrode region. At the base electrode an accumulation channel is formed and all charge carriers pass through nanometer-sized holes in the thin aluminum film.…”

Section: Electrical Stress Conditionsmentioning

confidence: 99%

Electrically Stable Organic Permeable Base Transistors for Display Applications

Dollinger

Iseke

Guo

et al. 2019

Adv Elect Materials

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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...

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Section: Electrical Stress Conditionsmentioning

confidence: 99%

Electrically Stable Organic Permeable Base Transistors for Display Applications

Dollinger

Iseke

Guo

et al. 2019

Adv Elect Materials

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“…The output characteristic in Fig. 1d shows a clear saturation behavior, although the channel length of this device is in the nm-range16. Typically, such short channel devices lose their saturation behavior due to short channel effects.…”

Section: Resultsmentioning

confidence: 90%

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime

Klinger

Fischer

Kaschura

et al. 2017

Sci Rep

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In spite of interesting features as flexibility, organic thin-film transistors have commercially lagged behind due to the low mobilities of organic semiconductors associated with hopping transport. Furthermore, organic transistors usually have much larger channel lengths than their inorganic counterparts since high-resolution structuring is not available in low-cost production schemes. Here, we present an organic permeable-base transistor (OPBT) which, despite extremely simple processing without any high-resolution structuring, achieve a performance beyond what has so far been possible using organic semiconductors. With current densities above 1 kA cm−2 and switching speeds towards 100 MHz, they open the field of organic power electronics. Finding the physical limits and an effective mobility of only 0.06 cm2 V−1 s−1, this OPBT device architecture has much more potential if new materials optimized for its geometry will be developed.

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“…Simulations reveal that this happens exactly when charge carrier accumulation starts at the bottom of the base layer. [10] Hence, it can be concluded that the anodization at 2 V creates a very dense oxide layer on top of the base layer that successfully blocks all leakage current.…”

Section: Resultsmentioning

confidence: 97%

“…The base leakage current (10 -10 A) is decreased by about 4 orders of magnitude compared to a naturally oxidized base in previous reports, [9,17] with the leakage current being suppressed below the measurement limit for an anodization voltage of 4 V. With the base current being that low and decoupled from the collector and emitter currents, the OPBT can now be regarded as a field effect-transistor, as already proposed by simulations. [10] Although, the transmission is increased due to the anodization, the on-current of the transistor is reduced for higher anodizing voltage. This effect probably originates from a lower electric base-emitter field across the oxide in combination with a reduced number of pinholes (discussed later in the manuscript).…”

Section: Resultsmentioning

confidence: 99%

Vertical Organic Thin‐Film Transistors with an Anodized Permeable Base for Very Low Leakage Current

Dollinger

Lim

et al. 2019

Advanced Materials

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The Organic Permeable Base Transistor (OPBT) is currently the fastest organic transistor with a transition frequency of 40 MHz. It relies on a thin aluminum base electrode to control the transistor current. This electrode is surrounded by a native oxide layer for passivation, currently created by oxidation in air. However, this process is not reliable and leads to large performance variations between samples, slow production and relatively high leakage currents. Here, we demonstrate for the first time that electrochemical anodization can be conveniently employed for the fabrication of high performance OPBTs with vastly reduced leakage currents and more controlled process parameters. Very large transmission factors of 99.9996% are achieved, while excellent on/off ratios of 5x10 5 and high oncurrents greater than 300 mA/cm² show that the C 60 semiconductor layer can withstand the electrochemical anodization. These results make anodization an intriguing option for innovative organic transistor design.Pre-peer reviewed version of communication published in Advanced Materials, March 2019 https://doi.

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Operation mechanism of high performance organic permeable base transistors with an insulated and perforated base electrode

Cited by 22 publications

References 22 publications

Electrically Stable Organic Permeable Base Transistors for Display Applications

Electrically Stable Organic Permeable Base Transistors for Display Applications

Organic Power Electronics: Transistor Operation in the kA/cm2 Regime

Vertical Organic Thin‐Film Transistors with an Anodized Permeable Base for Very Low Leakage Current

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