Paddy K. L. Chan, The University of Hong Kong
Oana Jurchescu, Wake Forest University
Ioannis Kymissis, Columbia University
Brendan T. O'Connor, North Carolina State University
BB2: Systems and Integration
Monday PM, November 30, 2015
Hynes, Level 2, Room 203
2:30 AM - *BB2.01
Stretchable and Ultraflexible Electronics for E-Textile and Wearable Devices
Takao Someya 1 Naoji Matsuhisa 1 Tsuyoshi Sekitani 1 2 Tomoyuki Yokota 1
1University of Tokyo Tokyo Japan2Osaka University Osaka JapanShow Abstract
The attractiveness of e-textile and wearable devices are their ease in collecting biological information in day-to-day lives and exercises. However, even with conductive fibers or threads, the conventional weaving method was not good enough to pattern fine electrodes and wires. This is why more simplified process, such as printing, to directly pattern durable and conductive materials on a fabric was widely awaited. We have developed novel ink that functions electronically, and succeeded in printing through one printing process a tough elastic conductor. This printable conductor keeps its high conductivity even when it is expanded more than 3 times in size. We printed elastic wires and electrodes with this ink on a fabric and achieved a textile electromyograph sensor. This easy to print textile bio-info sensor can be used in sports, healthcare and medicine.
3:00 AM - BB2.02
Large Area Organic Temperature Sensor Array: From Thermal Conductivity Measurements to Device Fabrication
Paddy K. L. Chan 1 Xiaochen Ren 1 Xinyu Wang 1
1Univ of Hong Kong Hong Kong Hong KongShow Abstract
In organic/metal hybrid materials, the thermal boundary conductance across the metal/organic interface plays a significant role in overall thermal conductivity of the film. The conductivity of the organic or hybrid thin film not only plays a critical role in the thermal stability of the organic devices, but also governs the heat transfer mechanisms. Here by embedding metal nanoparticles into organic semiconductor, we have successively developed a thermistor for direct temperature sensing. By integrating the thermistor with the active matrix organic transistor array, we fabricated a large area 16 × 16 temperature sensor which can be directly used for temperature mapping of objects with various shape. Simultaneously, we apply 3-omega; method to measure the effective conductivity of the thin film and the results are compared with the finite element modeling. By carefully controlling the concentration of the silver nanoparticles, we can modify the sensitivity of different temperature sensors. For a thin layer of Ag and intermixed with DNTT (10% volume ratio), the thermal conductivity decrease from 0.363W/m-K (pure DNTT) to 0.305W/m-K which shows the importance of the thermal boundary conductance. In the integrated temperature sensor array, the hyrbid thermistors are connected in series to the drain contacts and the whole array is developed on flexible substrate. By optimizing the anodization growth of the alumium oxide (AlOx) dielectric, the tempearture array can be powered under 5V with dynamic range higher than 10 bits, which clealy shows their capability in portable temperature sensing applications. The low voltage flexible thermal sensor array is suitable for portable electronic devices and potentially scale up for electronic skin applications. Other application directions such as health monitoring or use as surgery tools can be achieved.
3:15 AM - BB2.03
High Detectivity All-Printed Organic Photodiodes
Adrien Pierre 1 Igal Deckman 1 Pierre Balthazar Lechene 1 Ana Claudia Arias 1
1Univ of California-Berkeley Berkeley United StatesShow Abstract
Photodiodes with high specific detectivity, which entails high external quantum efficiency (EQE) and low dark current, and large pixel sizes enable optical systems capable of imaging lower light intensities. Additionally, the ability of a photodiode to operate under high electric fields at reverse bias increases the amount of photogenerated charge that may be capacitively stored during a single integration period, which is known as the well capacity. Using only the highly scalable printing techniques of blade coating and screen printing to deposit the layers on plastic, flexible organic photodiode arrays are reported with average specific detectivities of 3.45×1013 cmmiddot;Hz0.5middot;W-1 at a bias of -5 V. Polyethylenimine is blade coated over PEDOT:PSS to form the bottom cathode on these inverted devices, which exhibits excellent uniformity in work function modification on the microscale (20 meV standard deviation) as well as over centimetric areas. Furthermore, it is found that the polyethylenimine interlayer is not only essentially for lowering the work function of the electrode to increase EQE but also serves as a hole blocking layer to decrease the dark current density to an average of 150 pA/cm2. Photodiodes fabricated with a screen printed PEDOT:PSS top anode exhibit dark current shunt resistances an order of magnitude higher than devices fabricated using thermally evaporated top electrodes as a result of the creation of defects in the active layer which serve as leakage paths. This results in a lower dark current at high reverse biases for devices with a screen printed top anode than the devices with thermally evaporated metal electrodes. Additionally, these devices show excellent bias stress stability under high applied fields (88 kV/cm) and low variability, with a coefficient of variation of 15% in specific detectivity for 24 pixels across an array with perfect yield. Integration of these photodiodes with organic thin film transistor arrays and charge integrators will also be demonstrated.
3:30 AM - BB2.04
Hierarchical Photonic Surfaces Using Template Stripping of Colloidal Quantum Dot Films
Ferry Prins 1 David K. Kim 1 Eva De Leo 1 Kevin McPeak 1 David J. Norris 1
1ETH Zurich Zurich SwitzerlandShow Abstract
Colloidal quantum dots are highly versatile optoelectronic components that combine size- and shape-tunable properties with the attractiveness of cost-effective solution-phase processing. As such, they are ideal building blocks for the formation of artificial solids in which the colloidal assembly profits from the carefully engineered properties of the individual quantum dots. A variety of quantum-dot-based optoelectronic devices have been reported recently, including light-emitting diodes1 and lasers with tunable emission across the entire visible range,2 as well as demonstrations of efficient solar cells3 and photodetectors.4 It is interesting to consider complementing the nanoscale-structure of the quantum dot assembly with wavelength-scale patterning. This would allow for the creation of hierarchical photonic structures.
Here, we present a template stripping technique that allows for high-resolution wafer-scale patterning of colloidal quantum-dot films.5 We combine simple drop-casting of colloidal dispersions with template stripping using hard silicon templates with lithographically defined patterns. Using this technique, large-area patterns of arbitrary shapes can be transferred with high fidelity onto the quantum-dot film itself. We will show that carefully designed photonic patterns can significantly modify the optical properties of these films, yielding enhanced outcoupling of fluorescence and improved absorption of irradiation. Our technique is compatible with commonly used ligand-exchange strategies for improved electronic properties and can potentially be applied to other solution processable materials such as metallic nanoparticles or organic polymers.
We will discuss the significant improvements that patterned quantum-dot films can offer in the performance of light emitting and light harvesting optoelectronic devices.
(1) Mashford, B. S. et al. Nat. Photonics2013, 7, 407-412.
(2) Dang, C. et al. Nat. Nanotechnol.2012, 7, 335-339.
(3) Chuang, C.-H. M. et al. Nat. Mater.2014, 13, 796-801.
(4) Konstantatos, G. et al. Nature2006, 442, 180-183.
(5) Prins, F. et al. in preparation2015.
3:45 AM - BB2.05
Highly-Aligned, Invisible, Printed Ag Nanofiber Electrode Array
Yeongjun Lee 1 Sung-Yong Min 1 Su-Hun Jeong 1 Tae-Sik Kim 1 Juyeon Won 2 Hobeom Kim 1 Jae Kyeong Jeong 2 Tae-Woo Lee 1
1POSTECH Pohang Korea (the Republic of)2Inha University Incheon Korea (the Republic of)Show Abstract
Ag nanowires (AgNWs) have low sheet resistance and high optical transmittance and are therefore good candidates for use as an alternative to conventional transparent indium-tin-oxide (ITO) electrodes. However, use of conventional short AgNWs has allowed fabrication of only randomly-dispersed sheet-type transparent electrodes, so the approach it cannot take full advantage of nano-sized electrodes (nanoelectrode). Moreover, the conventional solution-dispersed AgNWs have the limitations such as low dispersion uniformity, poor surface roughness, high optical haze and low controllability, which should be resolved. Here, we report use of Electrohydrodynamic Nanowire Printing (ENP) as a simple, fast and inexpensive method to print Ag nanofibers (Ag NFs) for use as transparent electrode. ENP produces highly-aligned and individually position-controllable Ag NFs with average diameter of 695 nm and low resistivity ρ = 5.7 µOmega;#8729;cm, which is comparable with that of bulk Ag (ρ = 1.6 µOmega;#8729;cm). We fabricated various FETs including all-NF FETs (carrier mobility ~ 2.08 cm2middot;V-1middot;s-1) that use two strings of Ag NFs, one as a nano-sized source nanoelectrode and one as a drain nanoelectrode. We also demonstrated organic light emitting diodes (OLEDs), transparent heaters and touch screen panels, thereby proving the feasibility using of printed Ag NF transparent electrodes. ENP will be useful for fabrication of various kinds of future nanoelectronics.
4:30 AM - *BB2.06
High Performance Digitally Printed Electronic Systems
Gregory Lewis Whiting 1 David Schwartz 1 Tse Nga Ng 1 Ping Mei 1 Brent Krusor 1 Eugene Chow 1 JengPing Lu 1
1Palo Alto Research Center Palo Alto United StatesShow Abstract
Through the use of digital printing methods, custom electronic systems can be additively fabricated in an on-demand fashion. Many device types (logic circuits, sensors, memory, power sources, etc) can be printed entirely from solution-based inks of conductors, semiconductors, dielectrics and stimuli-responsive materials. However, all-printed systems incorporating these devices are often constrained in the appliations they can address by the performance of the printed circuits, which are typically limited by print resolution and materials properties. In order to best take advantage of the assortment of printed components available a hybrid approach that incorporates low-profile Si-CMOS components into the printed system can be used to provide a balance between electrical and mechanial performance, customizability and cost. Following this approach, examples of digitally fabricated hybrid electronic systems for wireless multimodal sensing will be described as will approaches for providing power to these distributed systems. Additionally, a print-like method of programmable micro-assembly to directly transport and orient large numbers of pre-fabricated silicon chips using electrostatic fields will also be discussed.
5:00 AM - BB2.07
Solution-Processed Radio Frequency Diodes Based on Co-Planar Asymmetric Nanogap Electrode Architectures
James Semple 1 Stephan Rossbauer 1 Dimitra Georgiadou 1 Thomas Anthopoulos 1
1Imperial College London London United KingdomShow Abstract
Envisaged as key enablers of molecular electronics, plasmonic and spintronic devices, nanogaop electrodes have become a growing area of research in recent years. Many routes towards such structures have been investigated, including mechanical break junctions, electromigration, oblique-angle shadow evaporation and electron beam lithography. However, such nanofabrication processes suffer from low throughput, poor scalability and multiple complex processing steps. Furthermore few of these methods can be readily applied to produce nanogaps between dissimilar electrodes, hence closing the door to the fabrication of devices that rely on ambipolar carrier injection (e.g. light-emitting diodes) or extraction (solar cells, photodetectors etc.).
Here, we present a unique technique, namely adhesion lithography (a-Lith), capable of fabricating such asymmetric nanogap structures, and doing so at an unprecedentedly large scale1. The process relies on the selective tuning of electrode surface energies using self-assembled monolayers (SAMs) and the application of adhesive forces. The bulk of the process is done via solution and features on the order of 10 nm with aspect ratios of over 106 have been demonstrated.
One such application of this structure is the co-planar nano-Schottky diode. The latter type of diodes may be fabricated by a single step deposition of the semiconductor material directly onto the nanogap electrode structures. The mismatch between electrode work functions allows current flow in one direction only, the small active area reduces device resistance, while the planar structure minimises device geometric capacitance. Thus we demonstrate devices with extremely high rectification ratio (>106) and minimal RC constants due to the co-planar device architecture. The result is the demonstration of nano-Schottky diode operating at radio frequencies (>20 MHz) while they can be made using various semiconductors, including low temperature (<200°C) solution processed ZnO as well as solution deposited C60. Such large-area, low-cost devices could be the ideal candidate for integration into printable RFID tags, and enablers of future technologies such as widespread RFID supply chain management and the Internet of Things.
1. Beesley, D. J.; Semple, J.; Jagadamma, L. K.; Amassian, A.; McLachlan, M. A.; Anthopoulos, T. D. Nature communications 2014, 5.
5:15 AM - BB2.08
Direct Printing of Sub-10mu;m Metallic Features Using Engineered Nanoporous Stamps
Sanha Kim 1 Hossein Sojoudi 1 2 Hangbo Zhao 1 Gareth McKinley 1 Karen Gleason 2 A. John Hart 1
1Massachusetts Institute of Technology Cambridge United States2Massachusetts Institute of Technology Cambridge United StatesShow Abstract
Direct printing of conductive inks made from metallic nanoparticles is an attractive approach for scalable low-cost manufacturing of flexible electronics, such as thin film transistors and transparent electrodes for organic displays and solar cells. Accordingly, the traditional methods including screen, gravure, offset, flexography, and inkjet printing have significant commercial uses. Although each method has its own characteristics and advantages, the common limitation in device fabrication is the printing resolution, limited to smallest feature size of approximately 20 mu;m. In case of flexography, the solid elastomeric stamps load a thin layer of ink on the top surfaces of the stamp features, which is prone to film instability and liquid spreading as feature size becomes smaller. For emerging applications of printed electronics such as high-resolution flexible displays or metal grid transparent electrodes, it is necessary to print conductive patterns in 1-10 mu;m size range.
We have developed a nanoporous stamp material enabling direct printing of electronic materials with micron-scale resolution. The stamps comprise vertically aligned carbon nanotubes (CNT “forests”) coated with poly(perfluorodecyl acrylate), (pPFDA), via initiated chemical vapor deposition. The stamp structures have high porosity (>90%), possess structural robustness against capillary forces upon liquid infiltration/evaporation, and are sufficiently compliant (elastic modulus of ~30 MPa) for conformal contact against the target substrate. For printing, the nanoporous stamps are used in the same way as the solid elastomeric stamps in flexography, as the ink is transferred from compliant and raised stamp structures to the target substrate via local contact. However, the high porosity of the new stamp allows the ink to be confined inside the microstructures. As a result, upon contact with the target substrate, ink is transferred locally via the porous surface, realizing excellent replication of stamp pattern with uniform thickness. Using the engineered CNT stamps, we demonstrate scalable patterning of silver nanoparticles approaching micrometer dimensions with high fidelity (e.g. sharp corner radius ~3 mu;m, fine edge roughness <1 mu;m, and uniform thickness <100 nm). After sintering, the silver patterns show maximum conductivity of ~4.0×107 S/m (~60% of bulk silver). Printed silver honeycomb patterns, with minimum linewidth of 3 mu;m, are also directly fabricated on glass plate and PET films. After annealing, this pattern exhibits ~89% transmission at 200-800 nm wavelength with 6.4-13.1 Omega;/#9633; sheet resistance, which is significantly lower than ITO (20-100 Omega;/#9633; over 80% transparency). We further discuss the contact and fluid mechanics of ink transfer, and analyze the potential for continuous operation of nanoporous stamps for micron-scale patterning at high speed (~m/s) which would overcome the mutual limitations of existing patterning methods for manufacturing of printed electronics.
5:30 AM - BB2.09
Printing Organic Semiconductors for Logic Circuits with Low Patterning Errors and Electrical Variability
Gaurav Giri 1 Steve Jeung Hoon Park 2 Zhenan Bao 3
1MIT Cambridge United States2Columbia University New York United States3Stanford University Stanford United StatesShow Abstract
Logic circuits are necessary to fulfill the vision of low cost, large area organic electronics, made with organic semiconductors (OSC) as the charge transfer layer. However, these circuits have stringent requirements. Primarily, all the thin film transistors (TFTs) participating in the circuit need to have a low variation in charge transfer characteristics (charge carrier mobility, threshold voltage, current, etc.). Additionally, organic circuits should be operated with low power consumption. To this end, research is being performed to pattern OSCs on the organic circuit to reduce parasitic current leakage. These twin requirements of low variability and OSC patterning set up conflicting goals, as the variability increases if each TFT is patterned individually. Moreover, patterning TFTs such that every TFT works, for the numerous TFTs required for logic circuits, is difficult with conventional methods such as ink jet printing due to patterning errors over large areas.
Here, we show a self-patterning method that does not require an extra patterning step to deposit the OSC layer onto the organic circuit. We have developed a surface functionalization procedure for a variety of oxide and metal surfaces, which, when paired with controlled solvent flow, can pattern OSCs in the TFT channel region only. Using this method, we show 100% viability of the patterned TFTs with low variability of charge carrier mobility and current. This method has been used to form logic gates and other organic circuits.
5:45 AM - BB2.10
High Mobility Low-Voltage Organic Transistors and Unipolar and Complementary Ring Oscillators on Plastic and Paper Substrates
Ulrike Kraft 1 2 Kazuo Takimiya 3 Florian Letzkus 4 Tarek Zaki 4 Joachim Burghartz 4 Edwin Weber 2 Hagen Klauk 1
1Max Planck Institute for Solid State Research Stuttgart Germany2TU Bergakademie Freiberg Freiberg Germany3RIKEN Advanced Science Institute Wako, Saitama Japan4Institute for Microelectronics (IMS Chips) Stuttgart GermanyShow Abstract
Potential applications of organic thin-film transistors (TFTs) are flexible displays, and the addition of active electronic anti-counterfeiting and tracking features to the existing passive security features on banknotes. For these applications, certain requirements such as low-voltage operation, a good shelf-life stability and high switching speeds have to be fulfilled not only on smooth Si wafers substrates used for material screenings but also on realistic plastic and paper substrates.
In this work, the low-voltage operation of the TFTs was enabled by employing a very thin hybrid gate dielectric consisting of a thin AlOx layer and a self-assembled monolayer of either an alkylphosphonic acid or a fluoroalkyphosphonic. The small thickness of the gate dielectrics leads to a large gate-dielectric capacitance and therefore allows operating voltages below 3V.
The utilized small-molecule semiconductors DNTT and its derivatives C10-DNTT and DPh-DNTT provide large carrier mobilities and an excellent air stability.
However, a good dynamic performance can be accomplished only by minimizing the parasitic capacitances, i.e., by employing TFTs with small lateral dimensions. In this work TFTs with channel lengths (L) ranging from 100µm down to 0.5µm were fabricated using high-resolution silicon stencil masks[3,4] that allow the accurate patterning of organic TFTs with small dimensions and an excellent parameter uniformity.
For DPh-DNTT TFTs on plastic substrates, carrier mobilities of 2.4cm2/Vs (L=100µm) and 0.6cm2/Vs (L=1µm) were measured. To test the suitability of the TFTs for real applications, we fabricated 11-stage unipolar and complementary ring oscillators on plastic substrates and on a 5-Euro banknote. For DPh#8209;DNTT TFTs with L=1µm on the plastic substrates, a signal delay per stage of 240ns was measured in ambient air at a supply voltage of 4V, which is the smallest signal delay reported to date for organic TFTs on flexible plastic substrates at operating voltages below 10V. For complementary circuits with p-channel DPh-DNTT TFTs and n#8209;channel PTCDI-(CN)2-(CH2C3F7)2 TFTs, the stage delay at 5V was as short as 3.1mu;s.
Despite the rough fibrous surface of the banknotes, the TFTs have mobilities up to 1.2cm2/Vs (p-channel TFTs) and 0.17cm2/Vs (n#8209;channel TFTs). The latter value is among the largest reported for organic n-channel TFTs on paper substrates. The thin gate dielectric allows the bending of the devices and in our tests no significant influence on the carrier mobility and the gate current was observed.. At 4 V, the measured stage delays are 2.5µs (unipolar) and 10µs (complementary). In comparison to earlier reports on organic circuits on paper substrates, these ring oscillators operate faster and at lower voltages.
 U. Kraft et al., Adv. Mater., 2015, 27, 207
 U. Kraft et al., DRC, Santa Barbara, USA, 2014,
 F. Ante et al., Small, 2012, 8, 73
 F. Letzkus et al., Microelectron. Eng., 2000, 53, 609
Monday AM, November 30, 2015
Hynes, Level 2, Room 203
9:00 AM - *BB1.01
Oxide and Organic TFTs on Thin Solution Cast Polymeric Substrates
Thomas N. Jackson 1
1Pennsylvania State Univ University Park United StatesShow Abstract
Flexible electronics has been demonstrated using both organic and inorganic semiconductors on a variety of substrates and using a wide range of fabrication approaches. Roll-to-roll processing has gained interest for high-throughput manufacturing, but presents challenges for in vacuum deposition, photolithography, and alignment between layers, complicated by substrate flatness and dimensional stability issues. Flexible substrates laminated onto rigid carriers (usually glass or Si) allow device fabrication using more standard equipment and processes, but often only partially solves substrate flatness and dimensional stability problems. We have used few micron thick