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Fast Flexible Transistors with a Nanotrench Structure.

Seo JH, Ling T, Gong S, Zhou W, Ma AL, Guo LJ, Ma Z - Sci Rep (2016)

Bottom Line: On the other hand, recent advances in nanoimprinting lithography (NIL) may enable the fabrication of large-area nanoelectronics, especially flexible RF electronics with finely defined patterns, thereby significantly broadening RF applications.A unique 3-dimensional etched-trench-channel configuration was used to allow for TFT fabrication compatible with flexible substrates.Optimal device parameters were obtained through device simulation to understand the underlying device physics and to enhance device controllability.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA.

ABSTRACT
The simplification of fabrication processes that can define very fine patterns for large-area flexible radio-frequency (RF) applications is very desirable because it is generally very challenging to realize submicron scale patterns on flexible substrates. Conventional nanoscale patterning methods, such as e-beam lithography, cannot be easily applied to such applications. On the other hand, recent advances in nanoimprinting lithography (NIL) may enable the fabrication of large-area nanoelectronics, especially flexible RF electronics with finely defined patterns, thereby significantly broadening RF applications. Here we report a generic strategy for fabricating high-performance flexible Si nanomembrane (NM)-based RF thin-film transistors (TFTs), capable of over 100 GHz operation in theory, with NIL patterned deep-submicron-scale channel lengths. A unique 3-dimensional etched-trench-channel configuration was used to allow for TFT fabrication compatible with flexible substrates. Optimal device parameters were obtained through device simulation to understand the underlying device physics and to enhance device controllability. Experimentally, a record-breaking 38 GHz maximum oscillation frequency fmax value has been successfully demonstrated from TFTs with a 2 μm gate length built with flexible Si NM on plastic substrates.

No MeSH data available.


Related in: MedlinePlus

DC characteristics of the TFTs with various trench gaps/channel lengths (Lch).Drain current versus drain voltage, Id − Vds, output curves are shown. All devices have 2 μm of gate length (Lg) and biased with Vgs ranging from 0 V to 1.5 V with a 0.3 V step (a) Devices with a 100 nm gap and a channel width and length of 20 μm and 100 nm. (b) Devices with a 200 nm gap and a channel width and length of 20 μm and 200 nm. (c) Devices with a 500 nm gap and a channel width and length of 20 μm and 500 nm. (d) Merged drain current versus gate voltage, Id − Vgs, transfer curves and transconductance (gm) with Vds = 0.1 V for these three devices. The two arrows show the directions of reducing Lch. (e) i) A microscope image of a bent array of TFTs and ring oscillators on a PET substrate. ii) A microscopic image of a single 5-stage ring oscillator under a flat condition. (f) Measured voltage–time characteristic of the 5-stage ring oscillator showing a fosc of 165 MHz and a td of 0.59 nsec.
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f4: DC characteristics of the TFTs with various trench gaps/channel lengths (Lch).Drain current versus drain voltage, Id − Vds, output curves are shown. All devices have 2 μm of gate length (Lg) and biased with Vgs ranging from 0 V to 1.5 V with a 0.3 V step (a) Devices with a 100 nm gap and a channel width and length of 20 μm and 100 nm. (b) Devices with a 200 nm gap and a channel width and length of 20 μm and 200 nm. (c) Devices with a 500 nm gap and a channel width and length of 20 μm and 500 nm. (d) Merged drain current versus gate voltage, Id − Vgs, transfer curves and transconductance (gm) with Vds = 0.1 V for these three devices. The two arrows show the directions of reducing Lch. (e) i) A microscope image of a bent array of TFTs and ring oscillators on a PET substrate. ii) A microscopic image of a single 5-stage ring oscillator under a flat condition. (f) Measured voltage–time characteristic of the 5-stage ring oscillator showing a fosc of 165 MHz and a td of 0.59 nsec.

Mentions: A comparison of the measured transfer and output characteristics for devices with various trench widths (i.e., channel length, Lch: 100 nm, 200 nm, and 500 nm) is shown in Fig. 4. The gate length (Lg) is 2 μm and the depth of trench for all fabricated TFTs were fixed to 2 μm and 200 nm, respectively. It is noted that the length of the channel region in the TFT is determined by the width of trench and, therefore, is not determined by the gate length (Lg) as it is in a conventional field-effect transistor. Because the channel length (Lch) is independent of the gate length (Lg), Lch can be very short – much shorter than Lg, as shown in the simulated results (Fig. 3). As shown in Fig. 4(a), the output curve (Ids − Vds) for a TFT with a 100 nm trench width showed poor saturation, which is attributed to the inaccurate trench etching to the desired depth as expected by the simulation in a Fig. 3(a). As the trench width increased to 200 nm and 500 nm (Fig. 4(b,c)), the drain currents were more saturated. The transfer curves for all three cases, with Vds = 0.1 V, are plotted in Fig. 4(d). The peak transconductance of the devices slightly increased from 79 μS to 90 μS, as the trench was narrowed from 500 nm to 100 nm, which was ascribed to the concentrated conductivity of the stronger field-effect in the channel region. As the simulation result shown in Fig. 3(b), TFTs with 100 nm trench widths had a relatively short channel region with a graded current density distribution which means that the electron movement could be easily limited by such a drastic change in the field-effect. On the other hand, TFTs with a 500 nm trench width had a uniform current density distribution. This phenomenon also agreed well with the calculated field-effect mobility. The field-effect motilities for the TFTs with trench widths of 100, 200, and 500 nm were 155, 250, and 460 cm2/V·s, respectively, and were extracted according to the equation (1) 23,


Fast Flexible Transistors with a Nanotrench Structure.

Seo JH, Ling T, Gong S, Zhou W, Ma AL, Guo LJ, Ma Z - Sci Rep (2016)

DC characteristics of the TFTs with various trench gaps/channel lengths (Lch).Drain current versus drain voltage, Id − Vds, output curves are shown. All devices have 2 μm of gate length (Lg) and biased with Vgs ranging from 0 V to 1.5 V with a 0.3 V step (a) Devices with a 100 nm gap and a channel width and length of 20 μm and 100 nm. (b) Devices with a 200 nm gap and a channel width and length of 20 μm and 200 nm. (c) Devices with a 500 nm gap and a channel width and length of 20 μm and 500 nm. (d) Merged drain current versus gate voltage, Id − Vgs, transfer curves and transconductance (gm) with Vds = 0.1 V for these three devices. The two arrows show the directions of reducing Lch. (e) i) A microscope image of a bent array of TFTs and ring oscillators on a PET substrate. ii) A microscopic image of a single 5-stage ring oscillator under a flat condition. (f) Measured voltage–time characteristic of the 5-stage ring oscillator showing a fosc of 165 MHz and a td of 0.59 nsec.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837400&req=5

f4: DC characteristics of the TFTs with various trench gaps/channel lengths (Lch).Drain current versus drain voltage, Id − Vds, output curves are shown. All devices have 2 μm of gate length (Lg) and biased with Vgs ranging from 0 V to 1.5 V with a 0.3 V step (a) Devices with a 100 nm gap and a channel width and length of 20 μm and 100 nm. (b) Devices with a 200 nm gap and a channel width and length of 20 μm and 200 nm. (c) Devices with a 500 nm gap and a channel width and length of 20 μm and 500 nm. (d) Merged drain current versus gate voltage, Id − Vgs, transfer curves and transconductance (gm) with Vds = 0.1 V for these three devices. The two arrows show the directions of reducing Lch. (e) i) A microscope image of a bent array of TFTs and ring oscillators on a PET substrate. ii) A microscopic image of a single 5-stage ring oscillator under a flat condition. (f) Measured voltage–time characteristic of the 5-stage ring oscillator showing a fosc of 165 MHz and a td of 0.59 nsec.
Mentions: A comparison of the measured transfer and output characteristics for devices with various trench widths (i.e., channel length, Lch: 100 nm, 200 nm, and 500 nm) is shown in Fig. 4. The gate length (Lg) is 2 μm and the depth of trench for all fabricated TFTs were fixed to 2 μm and 200 nm, respectively. It is noted that the length of the channel region in the TFT is determined by the width of trench and, therefore, is not determined by the gate length (Lg) as it is in a conventional field-effect transistor. Because the channel length (Lch) is independent of the gate length (Lg), Lch can be very short – much shorter than Lg, as shown in the simulated results (Fig. 3). As shown in Fig. 4(a), the output curve (Ids − Vds) for a TFT with a 100 nm trench width showed poor saturation, which is attributed to the inaccurate trench etching to the desired depth as expected by the simulation in a Fig. 3(a). As the trench width increased to 200 nm and 500 nm (Fig. 4(b,c)), the drain currents were more saturated. The transfer curves for all three cases, with Vds = 0.1 V, are plotted in Fig. 4(d). The peak transconductance of the devices slightly increased from 79 μS to 90 μS, as the trench was narrowed from 500 nm to 100 nm, which was ascribed to the concentrated conductivity of the stronger field-effect in the channel region. As the simulation result shown in Fig. 3(b), TFTs with 100 nm trench widths had a relatively short channel region with a graded current density distribution which means that the electron movement could be easily limited by such a drastic change in the field-effect. On the other hand, TFTs with a 500 nm trench width had a uniform current density distribution. This phenomenon also agreed well with the calculated field-effect mobility. The field-effect motilities for the TFTs with trench widths of 100, 200, and 500 nm were 155, 250, and 460 cm2/V·s, respectively, and were extracted according to the equation (1) 23,

Bottom Line: On the other hand, recent advances in nanoimprinting lithography (NIL) may enable the fabrication of large-area nanoelectronics, especially flexible RF electronics with finely defined patterns, thereby significantly broadening RF applications.A unique 3-dimensional etched-trench-channel configuration was used to allow for TFT fabrication compatible with flexible substrates.Optimal device parameters were obtained through device simulation to understand the underlying device physics and to enhance device controllability.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, University of Wisconsin-Madison, Madison, WI 53706, USA.

ABSTRACT
The simplification of fabrication processes that can define very fine patterns for large-area flexible radio-frequency (RF) applications is very desirable because it is generally very challenging to realize submicron scale patterns on flexible substrates. Conventional nanoscale patterning methods, such as e-beam lithography, cannot be easily applied to such applications. On the other hand, recent advances in nanoimprinting lithography (NIL) may enable the fabrication of large-area nanoelectronics, especially flexible RF electronics with finely defined patterns, thereby significantly broadening RF applications. Here we report a generic strategy for fabricating high-performance flexible Si nanomembrane (NM)-based RF thin-film transistors (TFTs), capable of over 100 GHz operation in theory, with NIL patterned deep-submicron-scale channel lengths. A unique 3-dimensional etched-trench-channel configuration was used to allow for TFT fabrication compatible with flexible substrates. Optimal device parameters were obtained through device simulation to understand the underlying device physics and to enhance device controllability. Experimentally, a record-breaking 38 GHz maximum oscillation frequency fmax value has been successfully demonstrated from TFTs with a 2 μm gate length built with flexible Si NM on plastic substrates.

No MeSH data available.


Related in: MedlinePlus