Organic transistors (OTFT) - the key to flexible electronics

Mike Banach, Technical Director

November 03, 2015

Today, the use of the word 'silicon' is almost synonymous with the electrical device that has made the material ubiquitous, namely the field effect transistor. 

At FlexEnable we're pioneering an alternative approach for making an organic transistor device using plastic materials which are cheap, unbreakable, and flexible. We're inspired by the fact that the simple transistor device has become foundation for all electronics, so a flexible version will have an endless number of applications. 

A transistor by definition is a simple electrical switch, but not every switch provides the same function. For example, microprocessors have millions of transistors wired together in series to create the complex decision hierarchy required to drive your phones and computers. In contrast, a flat panel display will also have millions of transistors fabricated on the surface of a piece of glass, but in this case an array of transistors (called a backplane) are operated in parallel to create a consistent image. The transistors in a backplane are specially designed for the sole function of controlling the performance of each pixel. 

ANOLEDMaking a backplane flexible is the key to making products that are no longer rigid, fragile, and is crucial to bringing more of our everyday surfaces to life.

However, not every backplane is the same, so the manufacturing process needs to be tailored for the specific application or 'frontplane' that the backplane is meant to control. This is easy to demonstrate when considering displays. More than 90% of the displays used today are made with liquid crystals (LCD) as the frontplane and they are controlled by voltage. The backplane for a LCD display includes one transistor on each pixel to switch it to the correct voltage during every drive cycle.

In contrast, organic light emitting (OLED) technology is an emerging frontplane, but these displays require a current instead of voltage for each pixel. A backplane for OLED will require multiple transistors for each pixel because it is more difficult to control a specific current than a voltage. 

Recently, we've been busy demonstrating that our backplanes are capable of driving both types of frontplanes - with our announcements on flexible OLCD (with Merck) and flexible OLED (with CPT).  

Of course the backplane is not only used to drive images, but it can also be used to read images. In this case, a sensitive material is used as the frontplane. For these applications the biggest consideration for the backplane is to efficiently capture the signal and transmit it before it is compromised. The FlexEnable backplane is ideal for such applications because our transistors are not very leaky, making it easier to read the actual signal over the 'noise' in the system. The optical sensors we have made in partnership with ISORG are perfect examples of how effective our backplanes can be when used in sensor arrays.

Backplane design is not easy, but our organic transistor technology provides a wonderful platform for multiple technologies. Do let us know if you have considered alternative applications for this type of technology -

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