Effects of self-assembled monolayer structural order, surface homogeneity and surface energy on pentacene morphology and thin film transistor device performance

Hutchins, Daniel; Weidner, Tobias; Baio, Joe E.; Polishak, Brent M.; Acton, Orb; Cernetic, Nathan; Ma, Hong; Jen, Alex K.‐Y.

doi:10.1039/c2tc00378c

Cited by 75 publications

(62 citation statements)

References 73 publications

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“…It is necessary to employ a suitable SAM to achieve high crystallility and carrier mobility in the OFETs. [ 14 ] To date, it is still a great challenge in the research fi eld to develop a universal high-k material which does not require SAM, and can be processed at moderate temperature, ambient air environment, and adjustable surface energy for both thermal evaporation and solution processing of organic semiconductors.To address these challenges, we recently reported a high-k (ε r = 11) barium strontium titanate (BST) thin fi lm treated by UV-Ozone and deposited by multi-layer spin coating deposition. [ 15 ] The high-k fi lms are spin coated in ambient air and heated to a temperature of around 85 °C during the UV-Ozone process.…”

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confidence: 99%

“…It suggests that the fresh deposited BST surface after UV-Ozone treatment is hydrophilic and has a high surface energy. By identifying the contact angles, the surface energy of the BST thin fi lms stored under different environment conditions and time are calculated by the well-established Wu (harmonic mean) method as follows: [ 14 ] γ γ γ γ…”

mentioning

confidence: 99%

“…Some of the SAMs would require relatively long preparation time [12][13][14] and usually the functional head groups of SAMs is dielectric specifi c. It is challenging to develop a universal SAMs suitable for different dielectric insulators. More importantly, the SAM also modifi es the surface energy of the dielectric and affects the crystallinity of the organic semiconductors.…”

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confidence: 99%

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Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

Wang

Ren

Fan

et al. 2014

Adv Materials Inter

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SAM is needed to reduce the leakage current through the gate and dielectric. Some of the SAMs would require relatively long preparation time [12][13][14] and usually the functional head groups of SAMs is dielectric specifi c. It is challenging to develop a universal SAMs suitable for different dielectric insulators. More importantly, the SAM also modifi es the surface energy of the dielectric and affects the crystallinity of the organic semiconductors. It is necessary to employ a suitable SAM to achieve high crystallility and carrier mobility in the OFETs. [ 14 ] To date, it is still a great challenge in the research fi eld to develop a universal high-k material which does not require SAM, and can be processed at moderate temperature, ambient air environment, and adjustable surface energy for both thermal evaporation and solution processing of organic semiconductors.To address these challenges, we recently reported a high-k (ε r = 11) barium strontium titanate (BST) thin fi lm treated by UV-Ozone and deposited by multi-layer spin coating deposition. [ 15 ] The high-k fi lms are spin coated in ambient air and heated to a temperature of around 85 °C during the UV-Ozone process. The UV emits at 184.9 nm and 253.7 nm under ambient air conditions converting oxygen into reactive O species, which then diffuse into the amorphous BST thin fi lm and reacts with the oxygen vacancies to form lattice oxygen. The reactive oxygen also removes the organic impurities in the fi lm, which results in a high quality amorphous BST thin fi lm with better stoichiometry. [ 16 ] The compatibility with ambient air environment, low processing temperature, and no SAM requirement suggest the BST dielectric has extremely high potentials to be applied in developing low cost OFETs on plastic fl exible substrates and have advantages over other polymers and inorganic materials. In the current study, we investigate the surface energy modifi cation effect by varying the storage environment and time of the BST thin fi lm in order to achieve a universal high-k material for OFET fabrications without using SAM. Based on the contact angle measurements, we calculated the surface energy and the wetting envelope of the BST high-k dielectric stored under different fi ve different conditions. The fresh BST with hydrophilic surface is suitable for spin coating or drop casting of organic semiconductor deposition where surface wetting is needed for the alignment of organic molecules. On the other hand, the BST thin fi lms stored under different conditions show different surface energy, which will directly affect the crystallinity of the organic semiconductors. On the current BST high-k dielectric without SAM and further optimization, dinaphtho[2,3-b:2′,3′-f ] thieno[3,2-b] thiophene (DNTT) and 6,13-Bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene) organic transistors with average mobility of 1.51 cm 2 V −1 s −1 and 0.11 cm 2 V −1 s −1 are formed by thermal evaporation and droplet-pinned crystallization (DPC) method (one of the solution processing methods...

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Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

Wang

Ren

Fan

et al. 2014

Adv Materials Inter

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“…Grain size of OSC films has significant effect on OFET characteristic [9,[17][18][19][20]. Generally, larger grains lead to better OFET performance because the transportation of charge carriers is facilitated by less grain boundaries [21,22].…”

Section: Introductionmentioning

confidence: 99%

Grain size adjustion in organic field-effect transistors for chemical sensing performance improvement

Fang

et al. 2018

Sci. China Mater.

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Various nanostructures of the organic semiconductor (OSC) films have been reported to enhance the organic field-effect transistors (OFETs) sensing performance. However, complicated fabrication processes hinder their applications. In this work, we have effectively enhanced the sensitivity of the OFET-based sensors only by adjusting substrate temperature in OSC preparation and surface treatment of the dielectric layer. The relative sensitivity of the device can be enhanced by 5 times. The flexible sensors with polymer dielectric also exhibit high sensitivity because the less smooth surface of the polymer provides the OSCs with smaller grain size. Therefore, this work reveals the trade-off effects of the OSCs grain size on both transistor characteristic and chemical sensing performance, and provides a simple and extensively applicable strategy for OFETs sensitivity improvement.

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“…Self‐assembled monolayers (SAMs) are now an ubiquitous tool for interface modifications to control and modulate a variety of devices such as hybrid and organic photovoltaics, light‐emitting diodes, and organic transistors . Recent progress has also expanded the role of SAMs from a passive interfacial modifier to potentially serve as an active device layer to replace traditional dielectrics and semiconductors in organic field‐effect transistors (OFETs).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Performance of Self‐Assembled Monolayer Field‐Effect Transistors with Top‐Contact Geometry through Molecular Tailoring, Heated Assembly, and Thermal Annealing

Cernetic

Weidner

Baio

et al. 2015

Adv Funct Materials

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5376 wileyonlinelibrary.com traditional dielectrics and semiconductors in organic fi eld-effect transistors (OFETs). For example, the development of hybrid dielectrics, which are comprised of an ultrathin high-k metal oxide layer in conjunction with an SAM, enables low-voltage high-performance operation of organic transistors. [16][17][18] Self-assembled monolayer fi eld-effect transistors (SAMFETs) are a promising concept that uses rationally designed π-conjugated SAMs as the semiconductor of a transistor. [19][20][21][22][23] This concept works in principle because charge transport in an organic semiconductor-based FET occurs in the fi rst few monolayers closest to the dielectric. [ 24,25 ] SAMFETs are believed to have a broad appeal for organic semiconductor device applications due to their low-cost processing, reduced material quantity needed compared to tradition organic thin fi lm transistors, and ability to be used toward fl exible electronics and sensing applications. Signifi cant progress has been made through molecular design and novel device architecture to achieve a state-of-the-art hole mobility of around 10 −2 cm 2 V −1 s −1 . In order to achieve further performance enhancement, it is critical to overcome a fundamental challenge of effi cient contact between the metal source/drain electrodes and SAM semiconductor in SAMFET devices. Effi cient contacts between SAM semiconductor and electrodes may have been enabled by Smits et al. through under-etching the electrodes allowing the SAM to form underneath or, as shown by Schmaltz et al. , through utilizing a secondary SAM to elevate the electrodes to allow edge-on contact with the SAM semiconductor core. [ 20,21 ] However, these reports utilize cumbersome and complicated device architectures that may make SAMFETs less appealing toward commercialization. Furthermore, little work has been done to examine the impact of SAM processing on molecular packing density.Herein we demonstrate top-contact bottom-gate low-voltage p-type SAMFETs with a hybrid hafnium oxide (HfO 2 ) dielectric that operates under a bias of −3 V and has a charge carrier mobility of 10 −2 cm 2 V −1 s −1 . Charge carrier mobility of the SAMFET is increased by over two orders of magnitude through the designed functional SAM terminal group that enables effi cient charge injection between metal electrode and SAM

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Effects of self-assembled monolayer structural order, surface homogeneity and surface energy on pentacene morphology and thin film transistor device performance

Cited by 75 publications

References 73 publications

Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

Low Cost Universal High‐k Dielectric for Solution Processing and Thermal Evaporation Organic Transistors

Grain size adjustion in organic field-effect transistors for chemical sensing performance improvement

Enhanced Performance of Self‐Assembled Monolayer Field‐Effect Transistors with Top‐Contact Geometry through Molecular Tailoring, Heated Assembly, and Thermal Annealing

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