Peter Andersson Ersman
Silicon-based electronics exhibit tremendous computational power. But applications requiring many contact pads, to form interfaces with sensors or displays, typically results in expensive chips due to the increased chip area. Here, we minimize the number of contact pads by combining conventional and printed electronic circuits.
The methods to manufacture organic electrochemical transistors (OECT) have been improved during the most recent years. The uniqueness of our development is that screen printing is used for the deposition of every layer, which results in a very simple manufacturing approach. The technology provides reliable devices with high manufacturing yield, and further miniaturization have resulted in a number of different screen printed integrated circuits, e.g. 4-1 multiplexers, 4-7 decoders and 7-bit shift registers.
The main objective is to minimize the number of contact pads on the silicon chip often used for addressing of peripheral devices, such as a display. Only two input signals are required in a 7-bit shift register (data + clock signal) to enable addressing of a 7-segment display. In addition to this, monolithic integration of screen printed digital circuits and electrochromic displays has also been obtained on flexible plastic substrates. The most complex circuits contain more than 100 OECTs, these results were published in Nature Communications (open access) in November 2019.
Yet another successful attempt has been carried out on the topic of monolithic integration of printed OECT-based digital circuits and electrochromic displays on flexible substrates, all manufactured by screen printing. The results, which were published in March 2020 in Flexible and Printed Electronics (open access), contain evaluations of various display driver circuits and their monolithic integration with electrochromic displays. In addition to this, high current throughput is one of the unique features of the OECT technology, and this is further demonstrated in the same article by controlling the light emission in traditional light emitting diodes (LED). The printed OECTs are capable of switching the light emission on and off, despite the high currents (typically several mA) that are flowing in such LEDs. The LEDs are properly addressed by a screen printed decoder circuit, and the light emission of the addressed LED is then controlled through an additional driver OECT, also manufactured by screen printing.
Monolithically integrated OECT-based circuits and electrochromic displays, all manufactured by screen printing on flexible substrates, enable a large number of future IoT applications, for example biosensor platforms for distributed healthcare, sensor platforms for monitoring of arbitrary sensors and electronic smart labels within packaging.
Additional articles related to screen printed OECTs and OECT-based circuits have been published recently. They are covering the topic of high yield manufacturing (99.7 % yield in a sheet containing 760 OECTs), active matrix addressed electrochromic displays, logic inverter circuit designs for operation at higher frequency (30 Hz) and lower voltages (1 V), OECTs manufactured by the combination of vapor phase polymerization (VPP) and screen printing, and OECTs used in functional electrical stimulation applications, see links under 'External press'.
All-printed OECTs have also been achieved by combining screen printing and aerosol jet printing. This results in OECT channels with much smaller area/volume, which in turn leads to improved switching performance. In one of the articles, we have now been able to demonstrate a propagation stage delay of only 1 ms when using such OECTs in inverter circuits.
OECTs can also be used as sensor devices. In this article we demonstrate heart beat monitoring by combining an OECT with a piezoelectric sensor screen printed on a tattoo paper substrate.
Printed integrated circuits
Development of components, circuits and printing methods
Swedish foundation for strategic research: Silicon-Organic Hybrid Autarkic Systems (SiOS), Eurostars Eureka: PROLOG , H2020: WEARPLEX, H2020: MITICS, Hybrid Electrochromic Materials for Energy Saving Displays