Researchers realize vertical-channel dual-base organic thin-film transistors for logic circuits.
Integrated circuits based on organic transistors are widely used in applications like paper displays. There have been many advancements in organic transistors since the past decade. One of the promising alternatives to conventional organic transistors are vertical-channel dual-gate organic thin-film transistors due to their short channel lengths and tunable threshold voltages.
However, due to the lack of appropriate p-type and n-type devices, developing complementary inverter circuits with these transistors is challenging. Researchers at Technische Universitat Dresden, Helmholtz-Zentrum Dresden Rossendorf (HZDR) and Northwestern Polytechnical University have developed vertical organic permeable dual-base transistors that could be integrated in logic circuits. In their paper, published in Nature Electronics, they explored the potential use of these transistors in complex integrated circuits.
The researchers have previously developed single vertical-channel thin-film transistors with an additional second gate and second dielectric, used to tune its threshold voltage. In their recent study, they evaluated the function and benefit of the vertical-channel dual-gate transistors in more complicated integrated circuits.
Researchers created integrated complementary inverters by connecting vertical n-channel organic permeable dual-base transistors (OPDBTs), and vertical p-channel organic permeable base transistors (OPBTs). The second gate in the OPDBTs can control the on and off-states of the transistors, thus influencing the states of the inverters.
“Based on the measurements we collected, we find that dual-base transistors enable a wide range of switching voltage controllability of a complementary inverter over 0.8 V, at an input voltage of <2.0 V, in a deterministic manner,” Erjuan Guo, one of the researchers who carried out the study, said. “We hence realized a switching voltage-tuneable inverter circuit using a VTH-tuneable n-type OPDBT and a p-type OPBT.”
The inverters developed by the researchers can maintain high/low output signals even at 10 MHz of the input signal. In addition, they have a very short rise and fall time of 5 ns and 6 ns respectively. They fabricated seven-stage complementary organic ring oscillators, integrating 7 inverters to demonstrate the advantages of vertical organic transistors for dynamic performance.
“At a supply voltage of 4.0 V, the measured signal propagation delay is 11 ns per stage for the ring oscillator is in a similar range as the rise and fall time of the single inverter,” Guo said. “These signal delays are short in comparison to those reported so far for organic ring oscillators on any substrate at supply voltages of less than 10 V.”
With this study, the researchers confirm the potential of using vertical organic transistors to fabricate high-frequency logic circuits. Though the transistors are not currently fast enough to be used in large-scale circuits, researchers are looking to increase the speed and reduce the size, so that device density can be increased.
