Printed electronics specialists PragmatIC recently demonstrated their latest fully functional ARM core that has excellent flexible properties. What challenges does flexible electronics present, what did PragmatIC demonstrate, and how could it finally pave the way towards future flexible electronics?

What challenges does flexible electronics present?

Flexible electronics is the development of flexible electronic components, and flexible electronics has many practical applications, including wearable technology, rugged sensors, and medical devices. However, creating flexible electronics presents engineers and researchers with many challenges. While some flexible electronics exist, most are cable connectors, antennas, or prototypes of individual components in laboratories.

The biggest challenge faced by flexible electronics is finding materials with electrical properties that can flex. Creating passive components is quickly done using flexible inks that can be printed onto all kinds of substrates (resistors are made using a narrowing of a conductor while capacitors are just two plates separated by a distance).

However, trying to develop active components (i.e. transistors) is another case as such devices consist of complex layers with tight constraints. For example, a MOSFET required a semiconductor layer to be doped with an insulating layer between it and the thin gate that controls the semiconductor channel. Any deformation to the MOSFET could change its conductive abilities, its gate charge, and its maximum ratings.

PragmatIC demonstrate a fully functional flexible ARM core microcontroller

PragmatIC is a UK semiconductor manufacturer that specializes in the research and development of flexible electronics. PragmatIC have been featured on Electropages previously when they were awarded a government grant of £1.3m to implement recycling schemes for disposable electronics.

While PragmatIC have demonstrated functioning circuits that are incredibly flexible, they have only recently shown for the first time a fully functioning ARM microcontroller entirely on a flexible substrate. The CPU is printed on a flexible substrate that the company calls “FlexARM”, and the CPU itself has 456 bytes of ROM and 128 bytes of RAM. The circuit integrates a total of 56,340 N-type transistors and resistors with a total logic gate count of over 18,000.

What makes the design intriguing is its use of a technology similar to NMOS logic. Each logic unit has a pull-up resistor that draws power when the associating transistor is turned on. As a result of using NMOS style logic, the device is only 1% energy efficient in computation. This use of NMOS style logic also demonstrates the challenges of printed electronics when trying to create complementary logic gates (i.e. P and N types working together to minimize static power consumption).

In terms of electrical performance, the CPU has a clock speed of 29kHz and consumes 21mW. The onboard ROM is not reprogrammable, but this is most likely due to the simplicity in implementing ROM over other memory technologies such as SRAM and FLASH. Furthermore, the CPU also has 28 pins for external connections, including 2 GPIO ports and measures only 9mm x 9mm.

The drop that starts the ripples

While the device produced by PragmatIC is highly energy inefficient and contains very few transistors compared to modern devices, there is no doubt whatsoever that this device is the spark that will ignite a race in flexible electronics. Of all researchers and engineers in flexible electronics, PragmatIC has achieved what no one else has been able to till this day; create a practical device.

Of course, the IC created by PragmatIC requires further development with a dire need for CMOS technology and reducing the size of transistors. Still, the very fact that a functioning, flexible computer has been constructed is a significant step in creating flexible electronics. The device developed by PragmatIC is already miles ahead of the Intel 4004 (the first CPU on the market), and that device was able to create a fully working 4-bit computer. The next decade could likely see flexible electronics move into the IoT and medical industries, and it is most likely that PragmatIC will be at the centre of this.