Imagine printing useful circuits that include switches, batteries, displays, sensors, and antennas on thin films, paper, foil, or plastic substrates — and producing them at high-speeds. A technology called print electronics (PE) can do exactly that and in nearly any shape or size. In fact, PE can generate permanent or disposable electronics in a fraction of the time it takes traditional methods to make circuitry with silicon chips and printed-circuit boards. Here's how it works.

PE uses high-speed printing presses to deposit functional materials including conductive, semiconductive, and dielectric inks. The process is sometimes called plastic or polymer electronics because organic materials make up some of the components. The most basic examples include printed antennas, conductive traces and electrochemical test strips. More complex devices and electronic circuits use multiple substrate layers, multiple function material layers, or printed structures on both sides of a single substrate.

Our proprietary process, for example, uses an environmentally friendly additive technology to form patterns by depositing special materials where needed. This contrasts with conventional, printed-circuit board and silicon-based electronics which use more expensive and complex lithography and subtractive processes. Such older technologies often involve hazardous substances including strong acids and solvents that generate waste and require special handling.

Design in new ways

PE allows designing in whole new ways. Replacing traditional discreet components such as resistors and capacitors with integrated PE versions reduces component bulk and makes possible new product form factors. Printing multiple components on a single substrate minimizes the number of manufacturing steps by eliminating pick-and-place operations. Designing with PE opens new realms of products such as flexible fingerprint sensors, proximity readers and I.D. cards, and smart bandages and patches for monitoring health metrics.

Also, because PE simplifies manufacturing from that of traditional electronics, designs can quickly move from prototype to high-volume production. Electronic designs can be changed rapidly without big scheduling ramifications. PE allows production of a wide range of practical items including test strips, battery testers, thin displays, and packaging enhancements that differentiate products. PE gives designers the flexibility of electronics on paper.

Applications

The PE industry is in its infancy and many more complex electronic devices, such as thin-film transistors, are still in development. Components including displays, sensors, and memory are also in early stages. That said, while print electronics has not yet reached the performance of silicon-based circuitry, it gives an affordable way to produce thin, flexible, disposable electronics. Best yet, it can work with traditional rigid circuitry such as ICs and ASICs to handle electronic “heavy lifting” and thus provide the best of both worlds. A few applications include:

Conformable flexible heaters to warm fluids or skin. Rethink using rubber or polyimide film substrates. Paper-thin materials and conductive inks can build ultra-thin heating elements with wide flexibility.

Keypads and membrane switches are made with conductive traces and materials. They are resistant to moisture, chemicals, and temperature extremes.

Optical displays and sensors are useful in disposables such as home pregnancy tests. Print active or passive displays in color or monochromatic. Output can come from sensors with an organic, LED printed with inks that change color and emit light.

Memory and data logging devices are made with thin, flexible, and disposable stand-alone rewriteable memory cells that make it easy to store and retrieve data on objects even if they have irregular shapes. PE works with active and passive logic devices as well as conventional ICs, ASICs, and other logic.

Disposable test strips can rely on electrochemical or electroconductive processes for diagnostic and therapeutic tasks. Consider PE for strips that monitor and analyze lead, ketones, or blood-glucose amounts. PE can produce strips that provide accurate quantitative measurements and in high volumes. Devices are affordable for clinic and home use.

Disposable electronic sensors and electrodes range from simple patches that attach to the skin, such as EKGs and TENS, to sophisticated resistive components. These disposables include electrochemical devices using biosensors based on amperometry, coulometry, or potentiometry. Flexible patches are capable of sensing pulse, moisture, pressure, heart rate, temperature, and other parameters. PE even allows adding thermal sensing or electrical stimulation for improved wound care.

RFID tags can be used to locate assets and track products. Many applications in labs, hospitals, and physician offices could benefit from the tags. Examples might include locating critical patient files, tracking and locating expensive monitors, supplies, and instrumentation, and ensuring all sponges and instruments are accounted for at the end of surgical procedures. RFID tags also work well for employee ID-security badges and on nametags also used to locate staff or patients. RFID tag antennas are currently printed, and fully printed tags are in development.

“Smart” packaging can track patient compliance. The Healthcare Compliance Packaging Council reports that patient non-compliance with prescribed drug regimens leads to more than 125,000 deaths/year and increases hospital admissions by as much as 10%/year. Pharmaceutical companies today are using PE in clinical drug trials to visually or audibly alert users when medicines should be taken and record when patients punch tablets through the blister packaging.

Similar technology also helps halt prescription-drug diversion, tampering, and counterfeiting by maintaining what's called an “e-pedigree.” This is an electronic record attached, for example, to a bottle of drugs that provides certificates of authenticity as the drug moves from manufacturers and distributors to pharmacies and hospitals.

PE in the future

New applications become possible as the technology and techniques evolve. One example is smart patches for diagnostic, monitoring, or therapeutic tasks. Here, smart bandages would transdermally deliver variable drug doses that are accurately timed and recorded. The bandages would also wirelessly transmit diagnostic data to a CPU or reader.

Other thin, disposable patches could let military health facilities sense and transmit heart rates, body temperatures, respiratory rates, blood-oxygen levels, and pulse waveforms of soldiers in the field. In fact, the DoD's Darpa is exploring this concept to report patient status and alert medics when measured parameters are outside prescribed values. These smart patches would sense and transmit physiological parameters to a handheld reader or store values using rewriteable flexible memory.

New materials in print electronics

Electronics manufacturers have been “printing” a variety of materials for several decades. However, new materials that can be printed and processed at much lower temperatures on flexible substrates are generating a lot of excitement in the field. Previously, printed silver had been used for many years but required curing at high temperatures (over 150C) to get adequate conductivity. In contrast, today's flake-based and nano-particle silver inks cure at low temperatures (less than 150C), suitable for flexible substrates such as PET and paper. These materials are processed on specialized roll-to-roll printing presses, significantly increasing production throughput as compared to older technologies.

Other interesting developments are in printable dielectrics. These materials too have been around for some time, but only recent UV-curable formulations support high-speed deposition. Forming insulating layers for conductive trace cross-overs and printing capacitors on flexible substrates are now feasible applications. And the addition of carbon-based inks for forming resistors provides all the necessary building blocks for RC circuits.

New materials will also soon allow flexible displays that are electrochromic (characterized by color change when voltage is applied), electrophoretic (where particles suspended in a liquid move in response to an electric field and change the visual appearance of the display), and electrowetting (made by applying a potential difference and changing a liquid's contact angle). These displays are all reflective. Emissive displays now use printable organic light-emitting-diode materials. Look for the use of these materials to expand on rigid substrates such as glass and clear plastics in cell phones and PDAs, and also move into flexible display media.

Many large chemical and materials companies now have significant programs in new materials for PE.

Other new materials include transparent conductors for security, touch screens, and tamper detection, and semiconductor materials for making thin film transistors. New sensor materials are also on the horizon.