Journal: Science Advances

Article Title: Flexible low-voltage high-frequency organic thin-film transistors

doi: 10.1126/sciadv.aaz5156

Figure Lengend Snippet: ( A ) Photograph of organic TFTs and circuits fabricated at a maximum process temperature of 100°C on a flexible, transparent PEN substrate. ( B ) Schematic cross section of the TFTs and chemical structures of the organic materials used in their fabrication: n- tetradecylphosphonic acid (TDPA) used for the self-assembled monolayer (SAM) in the hybrid aluminum oxide/SAM gate dielectric, PFBT used to treat the gold source and drain contacts to reduce the contact resistance and the small-molecule organic semiconductors DPh-DNTT and C 10 -DNTT. ( C ) Photograph of a TFT having a channel length of 8 μm, a total gate-to-contact overlap of 4 μm, and a channel width of 200 μm. ( D ) Literature overview of the width-normalized contact resistance ( R C W ) in organic TFTs. The dotted lines at 10 2 and 10 5 Ω·cm indicate the typical range of contact resistances reported for organic TFTs. ( E ) Literature overview of the signal propagation delay per stage (τ) of organic TFT–based ring oscillators as a function of supply voltage. ( F ) Literature overview of the highest voltage-normalized transit frequencies ( f T /V ) of organic TFTs fabricated on rigid and flexible substrates. The solid horizontal lines indicate the voltage-normalized transit frequencies of LTPS TFTs used in smartphone displays and of state-of-the-art low-temperature–processed IGZO TFTs; the dashed line indicates approximately the minimum requirement for mobile displays (3 MHz V −1 ). For references, see table S1. (A and C) Photo credit: James W. Borchert, Max Planck Institute for Solid State Research.

Article Snippet: This approach was used to fabricate all organic TFTs (see fig. S1) and circuits presented in this work on 125-μm-thick PEN sheets (Teonex Q65 PEN; provided by W. A. MacDonald, DuPont Teijin Films, Wilton, UK).

Techniques:

Journal: Science Advances

Article Title: Flexible low-voltage high-frequency organic thin-film transistors

doi: 10.1126/sciadv.aaz5156

Figure Lengend Snippet: ( A ) Measured transfer characteristics of a DPh-DNTT TFT fabricated on a PEN substrate having a channel length ( L ) of 8 μm, a total gate-to-contact overlap ( L ov,total = L ov,GS + L ov,DS ) of 4 μm, and a channel width ( W ) of 200 μm. ( B ) Square root of the absolute drain current and effective charge-carrier mobility (μ eff ) calculated from the transfer characteristics measured at a drain-source voltage ( V DS ) of −2 V as a function of the gate-source voltage ( V GS ). The blue dashed line is a guide to the eye, indicating the ideal quadratic dependence of the drain current in the saturation regime on the gate-overdrive voltage ( V GS -V th ). ( C ) Extraction of the subthreshold swing ( SS ) from the forward and reverse sweeps of the transfer curves. The average subthreshold swing of (59 ± 2) mV/decade is within measurement error of the limit set by the thermal voltage at the measurement temperature ( T ) of 292 K. The threshold voltage ( V th ), defined here as the gate-source voltage at which the drain current is 100 pA, is (−0.75 ± 0.01) V. ( D ) Measured output characteristics of the same TFT. ( E ) TLM analysis of the linear transfer characteristics of flexible DPh-DNTT TFTs with channel lengths ranging from 1 to 10.5 μm for four different gate-overdrive voltages. ( F ) Channel width–normalized contact resistance ( R C W ) and intrinsic channel mobility (μ 0 ) extracted from the TLM analysis and plotted as a function of the gate-overdrive voltage.

Article Snippet: This approach was used to fabricate all organic TFTs (see fig. S1) and circuits presented in this work on 125-μm-thick PEN sheets (Teonex Q65 PEN; provided by W. A. MacDonald, DuPont Teijin Films, Wilton, UK).

Techniques: Extraction

Journal: Science Advances

Article Title: Flexible low-voltage high-frequency organic thin-film transistors

doi: 10.1126/sciadv.aaz5156

Figure Lengend Snippet: ( A ) Static transfer characteristics of an inverter based on two DPh-DNTT TFTs in a biased-load circuit design fabricated on a flexible PEN substrate for a supply voltage ( V DD ) of 2 V and bias voltage ( V bia s ) of −1 V. The TFTs have a channel length ( L ) of 1 μm and a total gate-to-contact overlap of 4 μm. The insets show the circuit diagram and a photograph of the inverter. Photo credit: James W. Borchert, Max Planck Institute for Solid State Research. ( B ) Static transfer characteristics of the same inverter for bias voltages ranging from −1 to 0 V. The open circles indicate the trip voltage. ( C ) Dynamic characteristics of the inverter in response to a square-wave input signal with a frequency of 2 MHz, a duty cycle of 50%, and an amplitude of 2.5 V. Characteristic rise and fall time constants of the switching delays (τ rise , τ fall ) were determined by fitting simple exponential functions to the measured output waveform. ( D ) Rise and fall time constants measured for supply voltages ( V DD ) of 1.5, 2.0, and 2.5 V. The amplitude of the square-wave input signal was identical to the supply voltage, and V bias = −V DD for each measurement.

Article Snippet: This approach was used to fabricate all organic TFTs (see fig. S1) and circuits presented in this work on 125-μm-thick PEN sheets (Teonex Q65 PEN; provided by W. A. MacDonald, DuPont Teijin Films, Wilton, UK).

Techniques:

Journal: Science Advances

Article Title: Flexible low-voltage high-frequency organic thin-film transistors

doi: 10.1126/sciadv.aaz5156

Figure Lengend Snippet: ( A ) Circuit diagram and photograph of an 11-stage ring oscillator based on biased-load inverters fabricated on a PEN substrate. Photo credit: James W. Borchert, Max Planck Institute for Solid State Research. ( B ) SEM micrograph of the channel region of an individual C 10 -DNTT TFT in the ring oscillator. All TFTs in the circuit have a channel length ( L ) of 1 μm and a total gate-to-contact overlap ( L ov,total ) of 4 μm. ( C ) Measured output signal of the ring oscillator operated with a supply voltage ( V DD ) of 4.4 V. A signal-propagation delay per stage (τ) of 79 ns is determined by fitting a sine wave to the output signal. ( D ) Stage delay and equivalent frequency ( f eq = 1/2τ) plotted as a function of the supply voltage.

Article Snippet: This approach was used to fabricate all organic TFTs (see fig. S1) and circuits presented in this work on 125-μm-thick PEN sheets (Teonex Q65 PEN; provided by W. A. MacDonald, DuPont Teijin Films, Wilton, UK).

Techniques:

Journal: Science Advances

Article Title: Flexible low-voltage high-frequency organic thin-film transistors

doi: 10.1126/sciadv.aaz5156

Figure Lengend Snippet: ( A ) Photograph of an organic TFT designed for two-port network analysis fabricated on a PEN substrate. All TFTs considered here have a total gate-to-contact overlap ( L ov,total ) of 10 μm and a channel width ( W ) of 100 μm. Photo credit: James W. Borchert, Max Planck Institute for Solid State Research. ( B ) Circuit diagram of a two-port network with a TFT as the device under test. ( C ) Drain component of the total gate capacitance ( C GD ) normalized by the gate-to-drain overlap area ( WL ov,GD ) and plotted as a function of the measurement frequency ( f ) for all of the TFTs in the two-port network analysis. The gate-drain capacitance C GD was calculated from the measured admittance parameters (| Y 21 | = 2π fC GD ). ( D ) Magnitude of the small-signal current gain (| h 21 |) of TFTs with channel lengths ( L ) ranging from 0.7 to 10.5 μm and with nominally identical gate-to-source and gate-to-drain overlaps ( L ov,GS = L ov,GD ) plotted as a function of the measurement frequency. The transit frequencies ( f T ) are determined as the frequency at which | h 21 | = 0 dB (red line). ( E ) Transit frequency ( f T ) plotted as a function of the channel length ( L ). The red line is a fit of to the measurement data (blue circles), yielding a width-normalized contact resistance ( R C W ) of (10 ± 2) Ω·cm and an intrinsic channel mobility (μ 0 ) of (6 ± 1) cm 2 V −1 s −1 . ( F ) SEM micrograph of the channel region of an asymmetric DPh-DNTT TFT with a channel length ( L ) of 0.6 μm, a gate-to-source overlap ( L ov,GS ) of 1.7 μm, and a gate-to-drain overlap ( L ov,GD ) of 8.3 μm. ( G ) Measured small-signal current gain (| h 21 |) of the same TFT plotted as a function of the measurement frequency, indicating a transit frequency ( f T ) of 21 MHz. ( H ) Measured transfer characteristics and transconductance ( g m ) plotted as a function of the gate-source voltage of the same TFT.

Article Snippet: This approach was used to fabricate all organic TFTs (see fig. S1) and circuits presented in this work on 125-μm-thick PEN sheets (Teonex Q65 PEN; provided by W. A. MacDonald, DuPont Teijin Films, Wilton, UK).

Techniques: