Beverly Russo

Scalable printed electronics: an organic decoder addressing ferroelectric non-volatile memory

Scalable circuits of organic logic and memory are realized using all-additive printing processes. A 3-bit organic complementary decoder is fabricated and used to read and write non-volatile, rewritable ferroelectric memory. The decoder-memory array is patterned by inkjet and gravure printing on flexible plastics. Simulation models for the organic transistors are developed, enabling circuit designs tolerant of the variations in printed devices. We explain the key design rules in fabrication of complex printed circuits and elucidate the performance requirements of materials and devices for reliable organic digital logic.

Degradation mechanisms of organic ferroelectric field-effect transistors used as nonvolatile memory

Organic ferroelectric field-effect transistors were fabricated by inkjet printing for use as nonvolatile memory. Changes in device hysteresis were measured for 7 days to determine the limiting properties that restrict memory retention time. It was found that shifts in threshold voltage contributed to ∼55% of the reduction in transistor current, while decreased dielectric capacitance and reduced semiconductor mobility accounted for ∼30% and ∼15% of the current decay, respectively. The decrease in mobility and the shifts in threshold voltages are caused by remnant dipolar alignment in the ferroelectric insulator, and the reduction in gate capacitance is explained by injected charges in the ferroelectric dielectric. A method to calibrate and extract the input switching voltage is presented, and this calibration accounts for variations in device characteristics with time and allows the ferroelectric transistors to be used as analog memories.

Defect Identification in Large Area Electronic Backplanes

We describe a rapid testing system for active matrix thin-film transistor (TFT) backplanes which enables the identification of many common processing defects. The technique spatially maps the charge feedthrough from TFTs in the pixel and is suited for pixels with switched-capacitor architecture.

All Printed Thin Film Transistors for Flexible Electronics

Methods used to deposit and integrate solution-processed materials to fabricate thin film transistors by ink-jet printing are presented. We demonstrate successful integration of a complete additive process with the fabrication of simple prototype TFT backplanes on glass and on flexible plastic substrates, and we discuss the factors that make the process possible. Surface energy control of the gate dielectric layer allows printing of the metal source-drain contacts with gaps as small as 10 um as well as the polymer semiconductor whose electronic properties are very sensitive to surface energy. Silver nanoparticles are used as gate and data metals, and a polythiophene derivative (PQT-12) is used as the semiconducting layer, and the gate dielectric is a polymer. The maximum processing temperature used is 150°C, making the process compatible with flexible substrates. The ION/IOFF ratio is 105-106, and TFT mobilities of 0.05 cm2/Vs were obtained. The electrical stability of the all-printed transistors was compared to conventional fabrication methods and it is shown to be acceptable for array operation. Here we discuss the yield of the printing process and show arrays that are integrated with E-ink media to form flexible paper-like displays.

Flexible printed sensor tape based on solution processed materials

In this report, the fabrication of inkjet-printed complementary organic inverters was demonstrated. The acceleration sensors were integrated with printed inverters to enable amplification of sensor signals. This demonstration of sensors with amplifiers showed a potential printing method to fabricate low-cost, mechanically flexible sensor system from polymers.

Solution-Processed Memristive Junctions Used in a Threshold Indicator

Inkjet-patterned memristive metal/oxide/metal structures were characterized to infer ionic and electronic transport parameters such as mobility and ion distribution. The conductance change with respect to voltage and time was measured for an individual crossbar junction and for junctions that are connected in series. It was found that continuous dopant redistribution during voltage scans led to a peak in conductance. The mutable conductance of memristive devices was utilized to demonstrate a threshold indicator, in which the crossbar junctions were connected with a piezo sensor input and an electrophoretic display output. The memristive circuit would switch the color of display pixels, depending on the number of input pulses sensed by the piezo. The threshold indicator demonstrates that memristive junctions can be used as integral control switches. It is composed of passive circuit components and does not require an external battery.

44.3: Flexible Electrophoretic Displays with Jet‐Printed Backplanes

Flexible electrophoretic displays are demonstrated using all-additive solution-processed active-matrix backplanes. The conducting traces and the organic semiconductor for the pixel circuit were deposited by inkjet printing. Printed backplanes with smaller pixel size are desirable and the consequences of increasing the display resolution from 37 ppi to 74 ppi are discussed. Novel fabrication approaches for printed multi-layer pixel designs are presented.

Characterization of flexible image sensor arrays with bulk heterojunction organic photodiodes

A prototype of mechanically flexible photosensor arrays using organic bulk heterojunction photodiodes has been developed on plastic substrates. The integration of a 4 μm thick sensor layer onto a flexible amorphous silicon thin-film transistor backplane gave an image sensor array with 35% external quantum efficiency and noise equivalent power of 30 pW/cm2 at reverse bias voltage of -4 V. Sensor properties such as sensitivity and spatial resolution are determined and compared to those of amorphous silicon photodiodes.

Methods for fabrication of flexible hybrid electronics

Printed and flexible hybrid electronics is an emerging technology with potential applications in smart labels, wearable electronics, soft robotics, and prosthetics. Printed solution-based materials are compatible with plastic film substrates that are flexible, soft, and stretchable, thus enabling conformal integration with non-planar objects. In addition, manufacturing by printing is scalable to large areas and is amenable to low-cost sheet-fed and roll-to-roll processes. FHE includes display and sensory components to interface with users and environments. On the system level, devices also require electronic circuits for power, memory, signal conditioning, and communications. Those electronic components can be integrated onto a flexible substrate by either assembly or printing. PARC has developed systems and processes for realizing both approaches. This talk presents fabrication methods with an emphasis on techniques recently developed for the assembly of off-the-shelf chips. A few examples of systems fabricated with this approach are also described.

The Interplay of Materials in Printed Electronics

The fabrication of electronic circuits using printing methods carries many promises such as low cost and large-area manufacturing capability. However, a variety of new materials is introduced and these have to work together in order to be compatible with the overall processing steps and to deliver good device performance. Here, some of the aspects related to the gate dielectrics are discussed and device applications of printed electronics are presented.