This research paper proposes analytical models for top and bottom contact organic field effect tr... more This research paper proposes analytical models for top and bottom contact organic field effect transistors by considering the overlapping of source-drain (S/D) contacts on to the organic semiconductor layer and effective channel between the contacts. The contact effect is investigated in the proposed models and further verified through two-dimensional (2-D) numerical device simulation. The electrical characteristics are obtained from the linear to saturation regime and analytical outcomes are compared with the simulation and experimental results, which shows good agreement and thus validate the models. The extracted mobilities for top and bottom contact structure include 0.129 and 0.0019 cm2/Vs, and the device resistance as 2.25 and 450MΩ and the contact resistance as 2.25 and 450 MΩ μm2, respectively. The performance difference between top and bottom contact is attributed to the structural difference and morphological disorders of pentacene film around the contacts in bottom contact device which results in higher contact resistance and lower mobility as compared to the top contact device.
Hybrid organic-inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for... more Hybrid organic-inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for large-area, low-power microelectronic applications. We have used atmospheric pressure processes to deposit inorganic ZnO and organic diF TES-ADT semiconductor layers and an Al 2 O 3 gate dielectric. The organic semiconductor uses a contacttreatment-related microstructure that allows circuits to operate without directly patterning the organic layer. Using a simple 4-mask process with bifunctional Ti/Au contacts for both ZnO and organic transistors, 7-stage ring oscillators were fabricated and operated at >500 kHz corresponding to a propagation delay of <150 ns/stage at a supply bias of 35 V. These are the fastest organic-inorganic CMOS circuits reported to date.
CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by tra... more CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by transfer printing of p-type and n-type single crystalline ribbons of silicon. The gain and the sum of high and low noise margins of the inverters were as high as ∼150 and 4.5 V at supply voltages of 5 V, respectively. The frequencies of the ring oscillators reached 2.6 MHz at supply voltages of 10 V. These results, as obtained with devices that have relatively large critical dimensions (i.e., channel lengths in the several micrometer range), taken together with good mechanical bendability, suggest promise for the use of this type of technology for flexible electronic systems.
not seen. Using a lower estimate of the cluster mass, 2 £ 10 4 M ( (ref. 28), in stars sufficient... more not seen. Using a lower estimate of the cluster mass, 2 £ 10 4 M ( (ref. 28), in stars sufficiently young for the present analysis, I estimate that the true deficit beyond 150 M ( in R136 is roughly four stars-that is, the result in the present work is more statistically significant by this measure. If the deficit of massive stars in R136 is real, then it represents another measurement of the upper mass cut-off.
The possibility of using random networks or aligned arrays of single-walled carbon nanotubes (SWN... more The possibility of using random networks or aligned arrays of single-walled carbon nanotubes (SWNTs) as semiconducting or conducting thin-film-type materials in the emerging field of flexible and large-area electronics has recently attracted some attention. The unique electrical, mechanical, and thermal properties of SWNTs, as demonstrated pri-marily through studies of single-tube devices such as transistors, solar cells, logic gates, and ring oscillators, make SWNTs a potentially attractive building block for thin-film devices. The absence of dangling bonds makes it possible for SWNTs to exhibit good electrical characteristics on a wide range of substrates, including plastics. This feature, combined with the ability to print the tubes at room temperature using dry transfer processes or solution casting make SWNT films potentially attractive for large-area and flexible electronics. Recent reports demonstrate that thin-film field-effect transistors (FETs) based on random networks of SWNTs can be successfully fabricated on plastic substrates, and that the resulting devices can achieve good electrical, mechanical, and even optical (e.g., transparency) properties. Several major challenges must be overcome, however, in order to take full advantage of SWNT films for these applications. First, since as-grown carbon nanotubes are mixtures of metallic tubes and semiconducting tubes, it is necessary to be able to grow semiconducting tubes only, perhaps by selective catalysis or by plasma-enhanced chemical vapor deposition (CVD), or to remove metallic tubes, perhaps by electrical breakdown or chemical functionalization. Several groups are working on these and related approaches, as they relate to applications of SWNTs in thin-film electronics as well as many other application areas. A second challenge, which is mainly related to active device applications, involves the development of materials for gate dielectrics that can be used to achieve high-performance n-and p-channel operation in SWNT TFTs, with low hysteresis, good mechanical properties, and compatibility for low-temperature plastic substrates.
... of two identical inverters. As can be seen from the figure, the organic CMOS inverter feature... more ... of two identical inverters. As can be seen from the figure, the organic CMOS inverter features similar values for both noise margins, (NMH = VOH-VIH = 7.8V, NML = VIL-VIH = 6.7V), which is a typical result for CMOS inverters. ...
... In this letter we report organic-based CMOS inverters consisting of n-channel C60 and p-chann... more ... In this letter we report organic-based CMOS inverters consisting of n-channel C60 and p-channel pentacene TFTs. The C60 and pentacene TFTs had mobilities of 0.68 and 0.59 cm2/V s and threshold voltages of 0.80 and −0.84 V, respectively. ...
We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect tr... more We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect transistors based on the solution processable methanofullerene [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). The transistors are capable of operating in both the p-and n-channel regimes depending upon the bias conditions. However, in the p-channel regime transistor operation is severely contact limited. We attribute this to the presence of a large injection barrier for holes at the Au/PCBM interface. Despite this barrier the inverter operates in both the first and third quadrant of the voltage output versus voltage input plot exhibiting a maximum gain in the order of 20. Since the inverter represents the basic building block of most logic circuits we anticipate that other complementary-like circuits can be realized by this approach.
nature materials | VOL 2 | OCTOBER 2003 | www.nature.com/naturematerials T he main difficulty in ... more nature materials | VOL 2 | OCTOBER 2003 | www.nature.com/naturematerials T he main difficulty in achieving ambipolar transistor operation is the injection of holes and electrons into a single semiconductor from the same electrode. This electrode needs to have a workfunction that allows injection of holes in the highest occupied molecular orbital (HOMO) of the semiconductor, and the injection of electrons in the lowest unoccupied molecular orbital (LUMO). Consequently,this will result in an injection barrier of at least half of the bandgap energy for one of the carriers. To circumvent injection problems due to this barrier, in double-carrier devices, such as lightemitting diodes 1 and photovoltaic cells 2 , two different electrodes are used to allow injection or collection of holes and electrons.Alternatively, one-electrode material can be used in combination with two different semiconductors,where one has its HOMO level and the other its LUMO level aligned with the metal work function. The semiconductors can be spatially separated by evaporation techniques to form discrete n-type and p-type transistors. A summary of the state-of-the-art mobilities of discrete n-type and p-type organic transistors is presented in ref. 3. Discrete n-type and p-type transistors have been integrated into CMOS logic circuits 4 . Moreover, the two semiconductors can also be evaporated on top of each other, resulting in a heterostructure that exhibits ambipolar transistor behaviour 5,6 . However, to fully exploit the advantageous properties of organic molecules, such as ease of processing leading to low-cost, high-volume, large-area applications 7-9 , solution processing is required. Here we demonstrate ambipolar transistors using heterogeneous blends, consisting of interpenetrating networks of p-type and n-type semiconductors, as suggested by Tada et al. . The distinction between n-type and p-type organic semiconductors, however, is artificial because it depends on the position of the work function of the electrode relative to the HOMO and LUMO energies of the organic semiconductor. Ambipolar charge transport is an intrinsic property of pure organic semiconductors. We show that ambipolar transport is observed experimentally on reduction of the injection barriers by using low bandgap semiconductors. The transistors have been combined into CMOS-like inverters. An analytical model is presented that describes the details of the inverter transfer characteristics.
The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (P... more The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al 2 O 3 dielectric are reported. Saturation mobility of 0.38 cm 2 /V s, threshold voltage of 1 V, subthreshold swing of 0.6 V/decade, and on/off current ratio of about 10 8 have been obtained. Both depletion and enhancement mode inverter have been realized with the change of treatment method of hexamethyldisilazane on PEALD Al 2 O 3 gate dielectric. Full swing depletion mode inverter has been demonstrated at input voltages ranging from 5 V to − 5 V at supply voltage of −5 V.
The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense... more The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense current interest. Beyond having excellent insulating properties, such materials must meet other stringent requirements for optimum OTFT function: efficient low-temperature solution fabrication, mechanical flexibility, and compatibility with diverse gate materials and organic semiconductors. The OTFTs should function at low biases to minimize power consumption, hence the dielectric must exhibit large gate capacitance. We report the realization of new spin-coatable, ultrathin (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;20 nm) cross-linked polymer blends exhibiting excellent insulating properties (leakage current densities approximately 10(-)(8) Acm(-)(2)), large capacitances (up to approximately 300 nF cm(-)(2)), and enabling low-voltage OTFT functions. These dielectrics exhibit good uniformity over areas approximately 150 cm(2), are insoluble in common solvents, can be patterned using standard microelectronic etching methodologies, and adhere to/are compatible with n(+)-Si, ITO, and Al gates, and with a wide range of p- and n-type semiconductors. Using these dielectrics, complementary invertors have been fabricated which function at 2 V.
We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic se... more We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic semiconductor, perfluoropentacene. The transistor exhibits excellent electrical characteristics, with a high electron mobility of 0.22 cm 2 /(V s) and a good current on/off ratio of 10 5 . The electron mobility is comparable to the hole mobility of a pentacene OTFT. By combining the n-type perfluoropentacene and the p-type pentacene, we have fabricated ambipolar OTFTs and complementary inverter circuits. The OTFTs with heterostructures of the p-and n-type organic semiconductors can operate as an ambipolar device with high electron and hole mobilities of 0.042 and 0.041 cm 2 /(V s). The complementary inverter using an n-channel perfluoropentacene OTFT and a p-channel pentacene OTFT exhibits excellent transfer characteristics with a voltage gain of 45. A complementary inverter using the ambipolar OTFTs is also demonstrated.
We report on the fabrication and characterization of dual-gate pentacene organic thin-film transi... more We report on the fabrication and characterization of dual-gate pentacene organic thin-film transistors (OTFTs) with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al 2 O 3 as a bottom-gate dielectric and PEALD 200 nm thick Al 2 O 3 as a top-gate dielectric. The V th of dual-gate OTFT has changed systematically with the application of voltage bias to top-gate electrode. When voltage bias from À10 V to 10 V is applied to top gate, V th changes from 1.95 V to À9.8 V. Two novel types of the zero drive load logic inverter with dual-gate structure have been proposed and fabricated using PEALD Al 2 O 3 gate dielectrics. Because the variation of V th due to chemical degradation and the spatial variation of V th are inherent in OTFTs, the compensation technology by dual-gate structure can be essential to OTFT applications.
This research paper proposes analytical models for top and bottom contact organic field effect tr... more This research paper proposes analytical models for top and bottom contact organic field effect transistors by considering the overlapping of source-drain (S/D) contacts on to the organic semiconductor layer and effective channel between the contacts. The contact effect is investigated in the proposed models and further verified through two-dimensional (2-D) numerical device simulation. The electrical characteristics are obtained from the linear to saturation regime and analytical outcomes are compared with the simulation and experimental results, which shows good agreement and thus validate the models. The extracted mobilities for top and bottom contact structure include 0.129 and 0.0019 cm2/Vs, and the device resistance as 2.25 and 450MΩ and the contact resistance as 2.25 and 450 MΩ μm2, respectively. The performance difference between top and bottom contact is attributed to the structural difference and morphological disorders of pentacene film around the contacts in bottom contact device which results in higher contact resistance and lower mobility as compared to the top contact device.
Hybrid organic-inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for... more Hybrid organic-inorganic CMOS thin-film circuits are a simple, potentially low-cost, approach for large-area, low-power microelectronic applications. We have used atmospheric pressure processes to deposit inorganic ZnO and organic diF TES-ADT semiconductor layers and an Al 2 O 3 gate dielectric. The organic semiconductor uses a contacttreatment-related microstructure that allows circuits to operate without directly patterning the organic layer. Using a simple 4-mask process with bifunctional Ti/Au contacts for both ZnO and organic transistors, 7-stage ring oscillators were fabricated and operated at >500 kHz corresponding to a propagation delay of <150 ns/stage at a supply bias of 35 V. These are the fastest organic-inorganic CMOS circuits reported to date.
CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by tra... more CMOS inverters and three-stage ring oscillators were formed on flexible plastic substrates by transfer printing of p-type and n-type single crystalline ribbons of silicon. The gain and the sum of high and low noise margins of the inverters were as high as ∼150 and 4.5 V at supply voltages of 5 V, respectively. The frequencies of the ring oscillators reached 2.6 MHz at supply voltages of 10 V. These results, as obtained with devices that have relatively large critical dimensions (i.e., channel lengths in the several micrometer range), taken together with good mechanical bendability, suggest promise for the use of this type of technology for flexible electronic systems.
not seen. Using a lower estimate of the cluster mass, 2 £ 10 4 M ( (ref. 28), in stars sufficient... more not seen. Using a lower estimate of the cluster mass, 2 £ 10 4 M ( (ref. 28), in stars sufficiently young for the present analysis, I estimate that the true deficit beyond 150 M ( in R136 is roughly four stars-that is, the result in the present work is more statistically significant by this measure. If the deficit of massive stars in R136 is real, then it represents another measurement of the upper mass cut-off.
The possibility of using random networks or aligned arrays of single-walled carbon nanotubes (SWN... more The possibility of using random networks or aligned arrays of single-walled carbon nanotubes (SWNTs) as semiconducting or conducting thin-film-type materials in the emerging field of flexible and large-area electronics has recently attracted some attention. The unique electrical, mechanical, and thermal properties of SWNTs, as demonstrated pri-marily through studies of single-tube devices such as transistors, solar cells, logic gates, and ring oscillators, make SWNTs a potentially attractive building block for thin-film devices. The absence of dangling bonds makes it possible for SWNTs to exhibit good electrical characteristics on a wide range of substrates, including plastics. This feature, combined with the ability to print the tubes at room temperature using dry transfer processes or solution casting make SWNT films potentially attractive for large-area and flexible electronics. Recent reports demonstrate that thin-film field-effect transistors (FETs) based on random networks of SWNTs can be successfully fabricated on plastic substrates, and that the resulting devices can achieve good electrical, mechanical, and even optical (e.g., transparency) properties. Several major challenges must be overcome, however, in order to take full advantage of SWNT films for these applications. First, since as-grown carbon nanotubes are mixtures of metallic tubes and semiconducting tubes, it is necessary to be able to grow semiconducting tubes only, perhaps by selective catalysis or by plasma-enhanced chemical vapor deposition (CVD), or to remove metallic tubes, perhaps by electrical breakdown or chemical functionalization. Several groups are working on these and related approaches, as they relate to applications of SWNTs in thin-film electronics as well as many other application areas. A second challenge, which is mainly related to active device applications, involves the development of materials for gate dielectrics that can be used to achieve high-performance n-and p-channel operation in SWNT TFTs, with low hysteresis, good mechanical properties, and compatibility for low-temperature plastic substrates.
... of two identical inverters. As can be seen from the figure, the organic CMOS inverter feature... more ... of two identical inverters. As can be seen from the figure, the organic CMOS inverter features similar values for both noise margins, (NMH = VOH-VIH = 7.8V, NML = VIL-VIH = 6.7V), which is a typical result for CMOS inverters. ...
... In this letter we report organic-based CMOS inverters consisting of n-channel C60 and p-chann... more ... In this letter we report organic-based CMOS inverters consisting of n-channel C60 and p-channel pentacene TFTs. The C60 and pentacene TFTs had mobilities of 0.68 and 0.59 cm2/V s and threshold voltages of 0.80 and −0.84 V, respectively. ...
We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect tr... more We demonstrate a complementary-like inverter comprised of two identical ambipolar field-effect transistors based on the solution processable methanofullerene [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). The transistors are capable of operating in both the p-and n-channel regimes depending upon the bias conditions. However, in the p-channel regime transistor operation is severely contact limited. We attribute this to the presence of a large injection barrier for holes at the Au/PCBM interface. Despite this barrier the inverter operates in both the first and third quadrant of the voltage output versus voltage input plot exhibiting a maximum gain in the order of 20. Since the inverter represents the basic building block of most logic circuits we anticipate that other complementary-like circuits can be realized by this approach.
nature materials | VOL 2 | OCTOBER 2003 | www.nature.com/naturematerials T he main difficulty in ... more nature materials | VOL 2 | OCTOBER 2003 | www.nature.com/naturematerials T he main difficulty in achieving ambipolar transistor operation is the injection of holes and electrons into a single semiconductor from the same electrode. This electrode needs to have a workfunction that allows injection of holes in the highest occupied molecular orbital (HOMO) of the semiconductor, and the injection of electrons in the lowest unoccupied molecular orbital (LUMO). Consequently,this will result in an injection barrier of at least half of the bandgap energy for one of the carriers. To circumvent injection problems due to this barrier, in double-carrier devices, such as lightemitting diodes 1 and photovoltaic cells 2 , two different electrodes are used to allow injection or collection of holes and electrons.Alternatively, one-electrode material can be used in combination with two different semiconductors,where one has its HOMO level and the other its LUMO level aligned with the metal work function. The semiconductors can be spatially separated by evaporation techniques to form discrete n-type and p-type transistors. A summary of the state-of-the-art mobilities of discrete n-type and p-type organic transistors is presented in ref. 3. Discrete n-type and p-type transistors have been integrated into CMOS logic circuits 4 . Moreover, the two semiconductors can also be evaporated on top of each other, resulting in a heterostructure that exhibits ambipolar transistor behaviour 5,6 . However, to fully exploit the advantageous properties of organic molecules, such as ease of processing leading to low-cost, high-volume, large-area applications 7-9 , solution processing is required. Here we demonstrate ambipolar transistors using heterogeneous blends, consisting of interpenetrating networks of p-type and n-type semiconductors, as suggested by Tada et al. . The distinction between n-type and p-type organic semiconductors, however, is artificial because it depends on the position of the work function of the electrode relative to the HOMO and LUMO energies of the organic semiconductor. Ambipolar charge transport is an intrinsic property of pure organic semiconductors. We show that ambipolar transport is observed experimentally on reduction of the injection barriers by using low bandgap semiconductors. The transistors have been combined into CMOS-like inverters. An analytical model is presented that describes the details of the inverter transfer characteristics.
The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (P... more The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al 2 O 3 dielectric are reported. Saturation mobility of 0.38 cm 2 /V s, threshold voltage of 1 V, subthreshold swing of 0.6 V/decade, and on/off current ratio of about 10 8 have been obtained. Both depletion and enhancement mode inverter have been realized with the change of treatment method of hexamethyldisilazane on PEALD Al 2 O 3 gate dielectric. Full swing depletion mode inverter has been demonstrated at input voltages ranging from 5 V to − 5 V at supply voltage of −5 V.
The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense... more The quest for high-performance organic thin-film transistor (OTFT) gate dielectrics is of intense current interest. Beyond having excellent insulating properties, such materials must meet other stringent requirements for optimum OTFT function: efficient low-temperature solution fabrication, mechanical flexibility, and compatibility with diverse gate materials and organic semiconductors. The OTFTs should function at low biases to minimize power consumption, hence the dielectric must exhibit large gate capacitance. We report the realization of new spin-coatable, ultrathin (&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;20 nm) cross-linked polymer blends exhibiting excellent insulating properties (leakage current densities approximately 10(-)(8) Acm(-)(2)), large capacitances (up to approximately 300 nF cm(-)(2)), and enabling low-voltage OTFT functions. These dielectrics exhibit good uniformity over areas approximately 150 cm(2), are insoluble in common solvents, can be patterned using standard microelectronic etching methodologies, and adhere to/are compatible with n(+)-Si, ITO, and Al gates, and with a wide range of p- and n-type semiconductors. Using these dielectrics, complementary invertors have been fabricated which function at 2 V.
We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic se... more We report on n-channel organic thin-film transistors (OTFTs) based on the novel n-type organic semiconductor, perfluoropentacene. The transistor exhibits excellent electrical characteristics, with a high electron mobility of 0.22 cm 2 /(V s) and a good current on/off ratio of 10 5 . The electron mobility is comparable to the hole mobility of a pentacene OTFT. By combining the n-type perfluoropentacene and the p-type pentacene, we have fabricated ambipolar OTFTs and complementary inverter circuits. The OTFTs with heterostructures of the p-and n-type organic semiconductors can operate as an ambipolar device with high electron and hole mobilities of 0.042 and 0.041 cm 2 /(V s). The complementary inverter using an n-channel perfluoropentacene OTFT and a p-channel pentacene OTFT exhibits excellent transfer characteristics with a voltage gain of 45. A complementary inverter using the ambipolar OTFTs is also demonstrated.
We report on the fabrication and characterization of dual-gate pentacene organic thin-film transi... more We report on the fabrication and characterization of dual-gate pentacene organic thin-film transistors (OTFTs) with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al 2 O 3 as a bottom-gate dielectric and PEALD 200 nm thick Al 2 O 3 as a top-gate dielectric. The V th of dual-gate OTFT has changed systematically with the application of voltage bias to top-gate electrode. When voltage bias from À10 V to 10 V is applied to top gate, V th changes from 1.95 V to À9.8 V. Two novel types of the zero drive load logic inverter with dual-gate structure have been proposed and fabricated using PEALD Al 2 O 3 gate dielectrics. Because the variation of V th due to chemical degradation and the spatial variation of V th are inherent in OTFTs, the compensation technology by dual-gate structure can be essential to OTFT applications.
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