Flexible Circuits

Extending Electronic Functionality with Printed Electronics and Printed Memory

While silicon-based circuitry has dominated the electronics marketplace, an opportunity to extend electronic functionality to a whole new category of products has emerged with Printed Electronics.


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Less expensive and more flexible than silicon, Printed Electronics (PE) are rapidly gaining traction, enabling applications that would not be practical with conventional electronics. In August  2011, the independent research and analyst firm IDTechEx, estimated that the overall market for printed and potentially printed electronics will grow from $2.2 billion in 2011 to $44.25 billion by 2021.

PE refers to a class of electronics manufactured using high-volume printing processes, like those traditionally associated with the production of newspapers or magazines. As these devices are often manufactured on roll-to-roll processes, they are frequently seen in flexible form factors that would not be possible with conventional silicon.

Thinfilm Electronics has developed a non-volatile, rewritable printed memory that is commercially available in the form of stickers that can be attached to cards, toys, and other flat or smoothly curved surfaces. These flexible memory products based on the use of a ferroelectric polymer are among a new generation of commercially available PE that take advantage of printing’s ability to not only coat a surface, but also to create patterns on it. They are suited for consumer products and are currently being used to create new types of interactive toys and games. When used in conjunction with a reader/writer, toys and collectable cards become programmable by the child and can contain personalized skill levels, unique combinations of character properties, and inventory items.

As higher-capacity passive array memories become available, printed memories will meet the needs of secure archiving, ticketing and other applications that demand encryption, and, in time, will be integrated with other electronic components, to enable ID tags, sensor tags, disposable price tags and other smart tags that require rewritable data storage.

Memory devices are distinctly different from “identifiers” such as QRcodes, barcodes or conventional RFID.  Identifiers are essentially a fixed number that is used to look-up information in a database. While one might store a large number in a memory device, many applications will not require a unique identifier when data is stored directly on the object of interest. Memory is an essential part of most electronics. It is required for identification, tracking status and history, and is used whenever information is stored.

Standard Printed Memories

Thinfilm’s first printed memory product uses a single-line architecture. Essentially, a printed memory is layer of ferroelectric polymer sandwiched between two electrodes. Current passes between the electrodes, through the polymer memory film. Depending on whether the voltage is positive or negative, dielectric dipoles within the thin polymer layer align in one of two directions, creating binary ones and zeroes. The polymer is completely bi-stable, so when the voltage is removed the dipoles remain pinned. The ferroelectric cell can be “written” into two different stable states. This is depicted in the curve in Figure 1a. In aligning the dipoles, a sense amplifier, connected to the bottom electrode, detects the memory cell’s state and, using charge integrator circuitry, outputs a proportional voltage (Figure1b).

Figure 1a
Hysteresis curve (a) and ferroelectric cell connected to a charge t (b).

The Thinfilm-patented passive memory separates active logic circuitry from the memory cell. That is, the sticker can store data independent of the read-write device. Passive memories are read by being contacted by (or connected to) a separate read- and write-unit (R/W-unit). Both discrete electronics solutions and also an ASIC-based variant for 20-bit memories are available. The ASIC chip (Figure 2), implemented by using high voltage CMOS technology, is designed for reading and writing data into the printed memory cells and for communication to other electronics such as a microcontroller. The basic commands are “full memory read,” “full memory write,” “bit read” etc., and allow for easy communication via I2C or SPI to the remainder of the system.

Figure 2
The 20-bit memory controller ASIC.

Printed memories offer system cost advantages when the number of places you want to store data outnumber the number of places you want to read it. This architecture is highly suitable for applications where a designer wishes to store, cache, or transfer small bits of data across multiple objects. Because the stickers are low-cost and use no heavy metals, they can be applied to high-volume, disposable products.

Using Printed Memories

Thinfilm has developed a technology demonstration unit to illustrate one of the many ways printed memory stickers can be used in toy and game applications (Figure 3). The game device, which contains a display, microcontroller, etc., is preloaded with OBA, a demonstration game in which characters evolve as they collect eggs. The identity of the character (fish, camel, parrot or turtle) is coded on the card, and the right character is loaded when the game launches. The character’s status in the game, in terms of number of eggs collected, is stored on the game card. Such cards can be collected, traded and used across multiple systems. As a sticker, the memory can also be used on figurines, and a variety of contact mechanisms are available depending on the specific application and design.

The demonstrator is meant to show the key features of the technology, namely rewritability and non-volatility. However, it is also built to accommodate custom software, which a designer can load via USB.

Passive Array

The first products use a single-line design, in which one bottom electrode crosses multiple top electrodes. However, some memory applications, such as securing documents or identification cards, require a higher capacity than is practical with this design. For such applications, Thinfilm has demonstrated a passive array architecture in which two or more bottom electrodes cross two or more top electrodes

For example, a printed 40-bit memory consists of two bottom electrodes instead of one as in the current 20-bit memories. The electrodes form a grid, with the ferroelectric film sandwiched between. For the same number of contact pads as a standard memory, (22 for the 20-bit memory), the array architecture doubles the capacity.

Passive array memories use the same design rules and will be produced in the same efficient roll-to-roll processes as the 20-bit stand-alone memories in early 2012. A passive array architecture multiplies the capacity of the memory and will enable the creation of more compact, higher-density printed memories.

Passive array allows for very small cell size and, as with the single-line passive design, does not require transistors at the cell level. The passive array architecture maintains the separation of the memory from the read/write electronics.

Addressable Memory

While the passive memory design is attractive for its simplicity, the drawback is that storage capacity is directly correlated with the number of contact pads between the memory and the system using it. It also requires the use of external addressing logic, limiting the integration with other printed components

Thinfilm completed the design and with PARC, a Xerox Company, has demonstrated addressable memory, in which CMOS-like transistors are used as logic circuitry. Thinfilm is commercializing this technology as part of its 2012 roadmap. This design, which combines  memory technology with transistor technology developed by PARC, requires a larger area than the passive design but further reduces the cost of connecting the memory to standard electronics.

More importantly, though, the addressable memory is the first step toward integrated printed systems. With the addition of printed logic, Thinfilm and partner companies will be able to connect other printed technologies, such as antennas (to provide wireless read and write to the memory), simple displays and sensors. This integration opens the doors for fully printed wireless ID tags, sensor tags, disposable price labels and other smart objects, at a fraction of the cost of conventional silicon-based electronics.

Manufacturing Using Printing

In the late 1990s, standard semiconductor micro-fabrication techniques were used to manufacture ferroelectric memories, by sputtering and evaporating the electronic materials and patterning the memories using photolithography, which typically resulted in significant fabrication cost.

Today, Thinfilm devices can be produced using a high-volume, low-cost roll-to-roll printed production process. In the printing process, the bottom electrode is printed using direct gravure printing, the memory film is printed using micro gravure coating, and the remaining layers are printed using rotary screen printing.

Thinfilm memories are much more cost-effective and environmentally friendly due to the use of an additive process and less-costly deposition methods. In this process, the materials used can be cured and sintered at low temperatures, allowing for use of low-cost plastic substrates such as PET (Figures 4a and b). Additive printing allows material to be deposited only where it is needed, without requiring any material to be removed, as is done in conventional subtractive methods.

As such, mass production using printing techniques to manufacture electronic memory makes it possible to reduce the number of process steps, resulting in dramatically lower manufacturing costs, and also reduced environmental impact as compared to traditional semiconductor processes.

While Thinfilm is focused on printed devices, other applications of printed electronics include printed solar cells and organic light emitting diodes (OLED) for lighting and displays. Sensors, batteries and photovoltaic energy sources are also in the market or under development. To date, though, they have largely been stand-alone offerings. With continuing advances in device design, materials and manufacturing processes, devices like Thinfilm’s memory technology will open the door to new products and applications (Figure 5). Low-cost, flexible devices that have the capability to both store data locally and communicate with the infrastructure around them will be critical to enabling many different visions for “the Internet of things.” 

Figure 5
Thinfilm roadmap — Products.

Thinfilm Electronics

Oslo, Norway.

+47 23 27 51 59.