Reflective Polymer Coating For Microscale Electronic Communication

A polymer coating which allows a device’s electrical activity to be optically transmitted based on its transparency.
Problem:
Existing wireless microscale communication platforms, such as radio-frequency antennas and micro-LEDs, are limited in their large footprint requirements relative to the chip size, have challenging integration pathways with existing complementary metal oxide semiconductor (CMOS) generation, or require additional supporting structures on-chip. These issues reduce the electrical efficiency, manufacturability, and stability of these communication components.
Solution:
The technology outlines the development of a polymer coating that has a small footprint, low power requirements, and can be easily integrated into current CMOS fabrication workflows for microscale communication.
Technology:
A thin layer of the polymer PEDOT:PSS (Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate) is applied to a reflective metal electrode. This polymer is uniquely able to respond to its environment via its oxidation-reduction potential. A positive potential applied in an electrolyte solution to the PEDOT:PSS-coated electrode causes the PEDOT to oxidize and become transparent, while a negative potential causes it to reduce and become opaque. This modification allows the device’s electrical changes to be transmitted by transparency data points, which can enable bidirectional communication in a variety of wireless systems.
Advantages:

Small footprint - communication element is <10µm by <10µm by a few dozen nm
Power requirements are low -- in the microwatt range
Ability to operate at reasonable data rates (10kHz)
Has survived >1b on/off cycles without failure in biologically relevant settings
Can be an “add-on” to any CMOS chip using existing lithography techniques

Stage of Development:

Proof of Concept

Operation and fabrication of submillimeter polymer optical transmitters (SPOTs). (a) Concept operational diagram for an arbitrary microchip. A sensor makes a measurement, onboard electronics process and digitize the data, and the resulting voltage is applied to the SPOT (a working electrode coated in PEDOT:PSS) relative to a counter electrode in an electrolyte solution. The voltage modulates the stack’s reflectivity and hence the reflected light intensity. (b) Reduced/neutral (left) and oxidized/doped (right) states of PEDOT:PSS (∼45 nm)-Pt stack in 1×PBS, at applied potentials of −800 mV and +200 mV, respectively, relative to an Ag/AgCl counter electrode. The polymer shown is cross-linked by thermal treatment. (c) Demonstration of SPOTs at macroscopic and microscopic scales. Center images show reduced (left) and oxidized (right) states of a cm-scale chip featuring the University of Pennsylvania coat of arms, consisting of individual μm-sized SPOTs determined via Floyd–Steinberg dithering. Far left and right images show enlarged views of the pixelation of the dolphin’s eye in the reduced and oxidized states, respectively. (d) Schematic diagram showing fabrication protocol (vertical heights exaggerated): (1) Begin with bare metal electrode on a Si chip; perform O2 plasma cleaning. (2) Spincoat PEDOT:PSS and bake. (3) Sputter Al and Cu sequentially. (4) Spincoat photoresist. (5) Pattern photoresist. (6) Ion mill through Al, Cu, and PEDOT:PSS. (7) O2-plasma-ash away photoresist from working electrode. (8) Etch away Al and Cu from working electrode in dilute HCl. The device is now complete. Scale bars: (b) 10 μm; (c, center) 3 mm; (c, right) 300 μm.
Intellectual Property: