2.2. Interface Trapping Effects 211 3. High-k Dielectric Materials for OFETs 212 3.1. Inorganic Dielectrics 212 3.1.1. Aluminum Oxide 213 3.1.2. Tantalum Oxide 215 3.1.3. Titanium Dioxide 216 3.1.4. Hafnium Dioxide 217 3.1.5. Zirconium Dioxide 218 3.1.6. Cerium Dioxide 218 3.2. Organic Dielectrics 218 3.2.1. Polymer Dielectrics 218 3.2.2. Self-Assembled Monoand Multilayers 225 3.3. Hybrid Dielectrics 227 3.3.1. Polymeric-Nanoparticle Composites 227 3.3.2. Inorganic-Organic Bilayers 232 3.3.3. Hybrid Solid Polymer Electrolytes 235 4. Summary 235 5. Acknowledgments 236 6. References 236

High-k organic, inorganic, and hybrid dielectrics for low-voltage organic field-effect transistors.

http://ieeexplore.ieee.org/iel5/5/31324/01456901.pdf

Microelectronic circuits

Recently, the discovery of organometallic halide perovskites provides promising routes for fabricating optoelectronic devices with low cost and high performance. Previous experimental studies of MAPbI3 optoelectronic devices, such as photodetectors and solar cells, are normally based on polycrystalline films. In this work, a high-performance planar-type photodetector fabricated on the (100) facet of a MAPbI3 single crystal is proposed. We demonstrate that MAPbI3 photodetector based on single crystal can perform much better than that on polycrystalline-film counterpart. The low trap density of MAPbI3 single crystal accounts for the higher carrier mobility and longer carrier diffusion length, resulted in a significant performance increasement of MAPbI3 photodetector. Compared with similar planar-type photodetectors based on MAPbI3 polycrystalline film, our MAPbI3 single crystal photodetector showed excellent performance with good stability and durability, broader response spectrum to near-infrared region, about 10(2) times higher responsivity and EQE, and approximately 10(3) times faster response speed. These results may pave the way for exploiting high-performance perovskites photodetectors based on single crystal.

/pdf/high-performance-planar-type-photodetector-on-100-facet-of-4y953f1q8f.pdf

High-Performance Planar-Type Photodetector on (100) Facet of MAPbI3 Single Crystal.

Organic semiconductors are usually not thought to show outstanding performance in highly-integrated, sub 100 nm transistors. Consequently, single-crystalline materials such as SWCNTs, MoS2 or inorganic semiconductors are the material of choice at these nanoscopic dimensions. Here, we show that using a novel vertical field-effect transistor design with a channel length of only 40 nm and a footprint of 2 x 80 x 80 nm$^2$, high electrical performance with organic polymers can be realized when using electrolyte gating. Our organic transistors combine high on-state current densities of above 3 MA/cm$^2$, on/off current modulation ratios of up to 108 and large transconductances of up to 5000 S/m. Given the high on-state currents at yet large on/off ratios, our novel structures also show promise for use in artificial neural networks, where they could operate as memristive devices with sub 100 fJ energy usage.

Vertical, electrolyte-gated organic transistors: continuous operation in the MA/cm$^2$ regime and use as low-power artificial synapses

The conductivity of an $n$-type semiconductor has been calculated in the region of low-temperature $T$ and low impurity concentration ${n}_{D}$. The model is that of phonon-induced electron hopping from donor site to donor site where a fraction $K$ of the sites is vacant due to compensation. To first order in the electric field, the solution to the steady-state and current equations is shown to be equivalent to the solution of a linear resistance network. The network resistance is evaluated and the result shows that the $T$ dependence of the resistivity is $\ensuremath{\rho}\ensuremath{\propto}\mathrm{exp}(\frac{{\ensuremath{\epsilon}}_{3}}{\mathrm{kT}})$. For small $K$, ${\ensuremath{\epsilon}}_{3}=(\frac{{e}^{2}}{{\ensuremath{\kappa}}_{0}}){(\frac{4\ensuremath{\pi}{n}_{D}}{3})}^{\frac{1}{3}}(1\ensuremath{-}1.35{K}^{\frac{1}{3}})$, where ${\ensuremath{\kappa}}_{0}$ is the dielectric constant. At higher $K$, ${\ensuremath{\epsilon}}_{3}$ and $\ensuremath{\rho}$ attain a minimum near $K=0.5$. The dependence on ${n}_{D}$ is extracted; the agreement of the latter and of ${\ensuremath{\epsilon}}_{3}$ with experiment is satisfactory. The magnitude of $\ensuremath{\rho}$ is in fair agreement with experiment. The influence of excited donor states on $\ensuremath{\rho}$ is discussed.

Impurity Conduction at Low Concentrations.

The authors report the fabrication of vertical organic triodes operated in the pronounced saturation regions by using two back-to-back pentacene Schottky diodes. The device with an optimized 0.7nm LiF hole injection enhancement layer and a 70nm pentacene emitter can achieve an ultrahigh common-emitter current gain of 48 in the saturation region at a low applied voltage VCE of −4V and a base current density of 0.25mA∕cm2. In addition, the device exhibits a high output current density of 12.1mA∕cm2 and a high on/off current ratio of 103.

Vertical organic triodes with a high current gain operated in saturation region

Organic thin-film transistors (OTFTs), with the viewpoints of low cost/low temperature processing, mechanical flexibility, and large area coverage, have spurred tremendous interest within the development of consumable electronics and optoelectronics such as flat-panel display drivers, radio-frequency identification tags, smart cards, and sensors. (1-5) The typical architecture of OTFTs has adopted inorganic metal-oxide-semiconductor field-effect transistors in which the source and drain lie on the same plane above or below the semiconductor layer. Therefore, the performance of conventional TFTs is determined by two design parameters, the channel length (L) and field-effect mobility (mFE), in accordance with tSD ¼L 2 /(mFEVDD), where tSD is the source-drain response time and VDD the supply voltage. (6) Although, substantial progress has been achieved in developing new organic materials with higher mFE, typically confined to 1cm 2 V � 1 s � 1 , (7) for conventional OTFTs, they still meet the lower operation frequencies and the higher operation voltages for some applications, which are mainly due to the low carrier mobility of organic semiconductors, and their frequency responses were also determined by the capacitance of the gate dielectric used. The design of TFTs with high performance relies mainly on the channel dimensions, for example the channel length. Hence, varying the channel length is a critical parameter in enhancing the carrier-transport properties across the drain/source in planar-type TFTs. However, shortening the channel length suffers from the incapability of integrating organic devices into nanolithographic techniques. Moreover, the contact resistance of semiconductors/metals limits the performance of devices while shortening the channel length down to sub-micrometer scales. (8) An alternative approach to shorten the channel length is to adopt a vertical structure for transistors. (9-12) Since the conductive channel is in a perpendicular direction to the substrate, the channel length can be precisely controlled by organic-film thickness down to the micrometer or sub-micrometer regimes. Owingtothisadvantageoftheshortchannel length,theoperation frequency and the operation voltage can be dramatically improved, even when we use the existing organic semiconductors as channel materials. Accordingly, extensive progress has been achieved in the production of high-performance organic vertical-type transistors (OVTs) such as polymer grid triodes, (13) hot carrier transistors, (14,15) gate-source-drain transistors, (16,17) and metal-based organic transistors. (18) Although these OVTs present high device performances as compared to the conven- tional OTFTs, they still lack apparent saturation regions, which limit their use in low-power and high-frequency electronic applications. In this communication, we demonstrate a promising vertical-type transistor, organic base modulation triode (OBMT), which is fabricated employing two back-to-back diodes on a flexible plastic substrate. The device exhibits current modulations with apparent saturation whileapplying various supply voltages to the base electrode. The operation mechanism could be attributed to the part of the induced current that flows through the base electrode rather than recombining at the base electrode. The effective mobility of the device is investigated by fitting the current-voltage characteristics at high voltages to the space- charge limited current (SCLC) model. Since the OBMT exhibits an operation behavior similar to that of conventional OTFTs, an inverter operated at low supply voltages can also be achieved by integrating a p-channel OBMT with a load resistor; such an inverter circuit and their voltage transfer curves are also demonstrated.

https://ir.nctu.edu.tw:443/bitstream/11536/7237/1/000266287600014.pdf

Organic Base Modulation Triodes and Their Inverters on Flexible Substrates

Pentacene thin-film transistors operated at low voltages have been realized by employing hybrid dielectrics, poly(4-vinylphenol) (PVP)-capped MgO. The MgO film was deposited by reactive evaporation of magnesium in oxygen. The PVP layer plays a role in modifying the surface morphology of the MgO layer, and the images of atomic force microscopy for the PVP-capped MgO films show a root-mean-square roughness of 1 nm. The hybrid dielectric has a dielectric constant of 7.05 with a dielectric strength. The fabricated pentacene organic thin-film transistors exhibit a mobility of 0.66 cm 2 /V s, a threshold voltage of -2.67 V, and an on/off ratio of 10 3 .

Pentacene thin-film transistor with PVP-capped high-k MgO dielectric grown by reactive evaporation

In this letter, the characteristics of vertical organic triodes fabricated by using two copper phthalocyanine (CuPc) back-to-back Schottky diodes with different metal base thicknesses are reported. The vertical organic triodes exhibit pronounced saturation regions in the output current-voltage characteristics. The common-emitter current gain reduces with increasing the Al base thickness due to the increase of recombination current at the base end resulted from the reduction of opening voids in the Al metal film. The common-emitter current gain of the device with 4.5nm thick Al base reaches 1.9 at VCE=−6V and JB=2.5mA∕cm2.

https://ir.nctu.edu.tw:443/bitstream/11536/10919/1/000245690700112.pdf

Influence of thin metal base thickness on the performance of CuPc vertical organic triodes

In this letter, the authors investigate the promising vertical-type triodes based on small organic molecules and the related hot-carrier transport The devices show transistorlike characteristics, in which output current can be modulated by demanding different input currents on their thin metal base electrodes By using pentacene for the channel layer material and N,N′-di(naphthalen-l-yl)-N,N′-diphenyl-benzidine for the carrier energy-enhancing layer, the vertical-type hot carrier triodes exhibit a good current saturation with current gain of 238 for both the common-base and common-emitter configurations The mechanism of operation is proposed and examined by the basic electrical measurements

Meng-Chyi Wu

Papers

Vertical organic triodes with a high current gain operated in saturation region

Organic Base Modulation Triodes and Their Inverters on Flexible Substrates

Pentacene thin-film transistor with PVP-capped high-k MgO dielectric grown by reactive evaporation

Influence of thin metal base thickness on the performance of CuPc vertical organic triodes

All-organic hot-carrier triodes with thin-film metal base