A Pulse-Biasing Small-Signal Measurement Technique Enabling 40 MHz Operation of Vertical Organic Transistors

Abstract

Organic/polymer transistors can enable the fabrication of large-area flexible circuits. However, these devices are inherently temperature sensitive due to the strong temperature dependence of charge carrier mobility, suffer from low thermal conductivity of plastic substrates, and are slow due to the low mobility and long channel length (L). Here we report a new, advanced characterization circuit that within around ten microseconds simultaneously applies an accurate large-signal pulse bias and a small-signal sinusoidal excitation to the transistor and measures many high-frequency parameters. This significantly reduces the self-heating and therefore provides data at a known junction temperature more accurate for fitting model parameters to the results, enables small-signal characterization over >10 times wider bias I–V range, with ~105 times less bias-stress effects. Fully thermally-evaporated vertical permeable-base transistors with physical L = 200 nm fabricated using C60 fullerene semiconductor are characterized. Intrinsic gain up to 35 dB, and record transit frequency (unity current-gain cutoff frequency, fT) of 40 MHz at 8.6 V are achieved. Interestingly, no saturation in fT − I and transconductance (gm − I) is observed at high currents. This paves the way for the integration of high-frequency functionalities into organic circuits, such as long-distance wireless communication and switching power converters.

High‐Speed Organic Single‐Crystal Transistor Responding to Very High Frequency Band

“…Although the c i value measured at 1 kHz is used in this experiment, the dielectric constant likely increases at lower frequencies because of dipole orientation‐induced polarization derived from polar substituents of parylene, leading to a slight overestimation of the effective mobility. Nevertheless, the obtained cut‐off frequency of 38 MHz is the highest value reported to date for organic FETs ( Table 1 ), and approaches the best value of 40 MHz achieved in a vertical permeable base C 60 transistor . This is the first demonstration of an OFET responding to the VHF band from 30 to 300 MHz, which is beneficial for long‐distance wireless communication.…”

“…Nevertheless, the obtained cut-off frequency of 38 MHz is the highest value reported to date for organic FETs (Table 1), and approaches the best value of 40 MHz achieved in a vertical permeable base C 60 transistor. [25] This is the first demonstration of an OFET responding to the VHF band from 30 to 300 MHz, which is beneficial for long-distance wireless communication. Furthermore, the voltage-normalized cut-off frequency (f T /V in ) is an important index for a fair comparison because f T is proportional to the applied voltage.…”

Electrically Stable Organic Permeable Base Transistors for Display Applications

“…[1][2][3] This progress has mainly been enabled by a steady improvement in the charge carrier mobility. Particularly in their switching speed, measured by the transition frequency, which has increased into the tens of MHz regime.…”

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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. 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. 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.

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

“…The present record for f t of organic transistors is 40 MHz, enabled by a vertical transistor concept -the Organic Permeable Base Transistor (OPBT). [7][8][9] Its vertical conductive channel facilitates the transistor to carry on-current densities as high as 1 kA/cm². [8] Furthermore, utilizing the full overlap area of the electrodes simultaneously results in a minimal parasitic capacitance and ultimately into record-high f t .…”