Janos Veres

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.

From Printed Transistors to Printed Smart Systems

Printing as a manufacturing technique is a promising approach to fabricate low-cost, flexible, and large area electronics. Over the last two decades, a wide range of applications has been explored, among them displays, sensors, and printed radio-frequency identification devices. Some of these turned out to be challenging to commercialize due to the required infrastructure investment, accuracy or performance expectations compared to incumbent technologies. However, the progress in terms of material science, device, and process technology now makes it possible to target some realistic applications such as printed sensor labels. The journey leading to this exciting opportunity has been complex. This review describes the experience and current efforts in developing the technology at PARC, a Xerox Company. Printed smart labels open up low-cost solutions for tracking and sensing applications that require high volumes and/or would benefit from disposability. Examples include radiation tags, one-time use medical sensors, tracking the temperature of pharmaceuticals at the item level, and monitoring food sources for spoilage and contamination. Higher performance can be achieved with printed hybrid electronics, integrating microchip-based signal processing, wireless communication, sensing, multiplexing, as well as ancillary passive elements for low-profile microelectronic devices, opening up further applications. This technology offers custom circuitry for demanding applications and is complementary to mass printed transistor circuits. As an example, we describe a prototype sense-and-transmit system, focusing particularly on issues of integration, such as impedance matching between the sensor and circuits, robust printed interconnection of the chips, and compatible interface electronics between printed and discrete parts. Next-generation technologies will enable printing of entire smart systems using microchip inks. A new printing concept for the directed assembly of silicon microchips into functional circuits is described. The process is scalable and has the potential to enable additive, digital manufacturing of high-performance electronic systems.

Printed dose-recording tag based on organic complementary circuits and ferroelectric nonvolatile memories

We have demonstrated a printed electronic tag that monitors time-integrated sensor signals and writes to nonvolatile memories for later readout. The tag is additively fabricated on flexible plastic foil and comprises a thermistor divider, complementary organic circuits, and two nonvolatile memory cells. With a supply voltage below 30 V, the threshold temperatures can be tuned between 0 °C and 80 °C. The time-temperature dose measurement is calibrated for minute-scale integration. The two memory bits are sequentially written in a thermometer code to provide an accumulated dose record.

Utilizing high resolution and reconfigurable patterns in combination with inkjet printing to produce high performance circuits

Inkjet printing on pre-fabricated high-resolution substrate is developed to improve the operational speed of printed organic transistors. The high-resolution features are designed to define transistor critical dimensions, while maintaining the flexibility to incorporate different circuit constructions. Logic gate and ring oscillator circuits fabricated by inkjet printing on the high-resolution substrate are demonstrated, to show that the same high resolution pattern can be adapted for constructing different electronic circuits.

Pulsed voltage multiplier based on printed organic devices

To enable the integration of components with different supply voltage requirements, and to optimize power consumption in printed flexible electronics, we demonstrate an inkjet-printed pulsed voltage multiplier that boosts the voltage at specific circuit nodes above the supply voltage. A five-stage pulsed voltage multiplier is shown to provide an output voltage up to 18 V from a supply voltage of 10 V, with minimum 10 ms pulse rise time for a 70 pF load. This circuit allows a single power source to deliver multiple voltage levels and enables integration of low-voltage logic with components that require higher operating voltage. A key requirement for the pulsed voltage multiplier circuit is low device leakage to boost the output voltage level. To this end, the composition of the transistor semiconducting layer is modified by blending an insulating polymer with the small molecule semiconductor. This modification allows control over the transistor turn-on voltage, which enables low leakage current required for operation of the circuit.

Persistent photoconductivity effects in printed n-channel organic transistors

Persistent photoconductivity of top-gate n-type organic transistors is investigated. The irradiation of green light leads to a negative shift in transistor threshold voltage and an increase in sub-threshold current. These light-induced effects are enhanced when the gate is negatively biased during the light irradiation, and the recovery process is faster at 60 °C than at 25 °C. After storage in dark, full recovery is obtained for a transistor printed with a neat semiconductor, whereas for the device printed with a solution of the same semiconductor mixed with an insulator, only partial recovery is observed after four days at room temperature. Other stress conditions (irradiation with a positive gate bias, irradiation without bias, and bias under dark) do not change the threshold voltage or the sub-threshold current significantly. We attribute this photo phenomenon to holes trapped and released at the dielectric/semiconductor interface and a smaller number of positive fixed charges generated in the bulk of...

Open and closed loop manipulation of charged microchiplets in an electric field

We demonstrate the ability to orient, position, and transport microchips (“chiplets”) with electric fields. In an open-loop approach, modified four phase traveling wave potential patterns manipulate chiplets in a dielectric solution using dynamic template agitation techniques. Repeatable parallel assembly of chiplets is demonstrated to a positional accuracy of 6.5 μm using electrodes of 200 μm pitch. Chiplets with dipole surface charge patterns are used to show that orientation can be controlled by adding unique charge patterns on the chiplets. Chip path routing is also demonstrated. With a closed-loop control system approach using video feedback, dielectric, and electrophoretic forces are used to achieve positioning accuracy of better than 1 μm with 1 mm pitch driving electrodes. These chip assembly techniques have the potential to enable future printer systems where inputs are electronic chiplets and the output is a functional electronic system.

Challenges and opportunities in flexible electronics

Flexible electronics has an exciting potential for enabling roll-able, foldable displays, smart patches and smart packaging on paper and plastic substrates. Many of these applications are relatively large area and match well with thin film deposition and patterning processes. The idea of printing sensors and transistors has attracted many companies because large area electronics can be fabricated roll-to-roll at low temperatures on plastic substrates. It has become apparent that fully printed electronic systems have limitations in performance today. More recently, there has been a focus on the integration of large area, flexible electronics with chips. The resulting technologies now enable specialized smart labels, chemical sensors in cold chain logistics and wearables.

Flexible Hybrid Electronic Circuits and Systems

Printed organic electronics are being explored for a wide range of possible applications, with much of the current focus on smart labels, wearables, health monitoring, sensors and displays. These applications typically integrate various types of sensors and often include silicon integrated circuits (IC) for computation and wireless communications. Organic thin film transistors (TFT), particularly when printed, have performance and yield limitations that must be accommodated by the circuit design. The circuit design also needs to select sensor technology, ICs and other circuit elements to integrate with the TFTs and match the functional and performance requirements of the application. This paper describes organic TFT properties and strategies for circuit and sensor design, with examples from various sensor systems.

Micro chiplet printer for micro-scale photovoltaic system assembly

The micro-CPV concept uses an array of micro unit cells (or elements) such that the material usage, weight, and the required structural strength can all be scaled down favorably. Unfortunately, one of the essential unfavorable scaling factors is the assembly cost due to the many micro scale components that must be deposited, positioned, oriented, and connected over large areas. By using a dynamic electric field template, we successfully demonstrate chiplet printing - assembling a desired solar cell chip at a designated location with well controlled orientation. Xerographic printing systems utilizing this method can be extended to provide high-throughput, on-demand heterogeneous assembly of micro-CPV systems.