TMOS researchers have developed a proof-of-concept technology that could pave the way for next-generation displays to supersede LCDs and LEDs, enabling screens and electronic devices to become thinner, offer higher resolution and be much more energy efficient.

The team included Centre Director Dragomir Neshev (Australian National University) and Associate Investigators Andrey Miroshnichenko (University of New South Wales) and Mohsen Rahmani (Nottingham Trent University). Their new ‘metasurface’ technology, detailed in Light: Science & Applications, offers significant benefits over current liquid crystal displays (LCDs).

The metasurfaces are 100-times thinner than liquid crystal cells, offer a tenfold greater resolution and could consume less energy.

Today’s screen display market offers a large range of choices, each with its pros and cons. However, factors including production costs, lifespan and energy consumption have kept LCD technology the most dominant and popular technology for screens such as TV sets and monitors.

Liquid crystal cells are responsible for switching the transmitted light on and off and are constantly lit by a backlight, with polarising filters in the front and behind the pixels, forming a cross-polarised setup. They determine the dimension of pixels – the resolution – and play a significant role in managing the device’s power consumption.

The newly engineered metasurface cells, which have tunability and extraordinary light scattering properties, would replace the liquid crystal layer and would not require the polarisers, which are responsible for half of wasted light intensity and energy use in displays.

“Our pixels are made of silicon, which offers a long life span in contrast with organic materials required for other existing alternatives. Moreover, silicon is widely available, CMOS* compatible with mature technology, and cheap to produce,” said Professor Andrey Miroshnichenko.

“We hope this development could generate a frontier technology in new flat screen displays, which had a global market value of about $117 billion in 2020.”

Professor Dragomir Neshev said the capability of conventional flat screen displays has reached its peak and is unlikely to significantly improve in the future due to multiple limitations. “Today there is a quest for fully solid-state flat display technology with a high-resolution and fast refresh rate. We have designed and developed metasurface pixels that can be ideal for the next-generation display.”

“Unlike liquid crystals, our pixels do not require polarised lights for functioning, which will halve screens’ energy consumption.”

Khosro Zangeneh Kamali, a PhD scholar at ANU and the first author of the study, said metasurfaces are proven to exhibit extraordinary optical behaviour. “Inventing an effective way to control metasurfaces is still a subject of heavy research. We have proposed electrically tunable silicon nanostructures, which is a versatile platform for programmable metasurfaces.”

“We have paved the way to break a technology barrier by replacing the liquid crystal layer in current displays with a metasurface, enabling us to make affordable flat screens liquid crystal-free,” said Prof. Mohsen Rahmani. “The most important metrics of flat panel displays are pixel size and resolution, weight and power consumption. We have addressed each of these with our meta-display concept.

“Most importantly, our new technology can lead to a huge reduction of energy consumption – this is excellent news given the number of monitors and TV sets being used in households and businesses every single day. We believe it is time for LCD and LED displays to be phased out in the same way as former cathode ray tube (CRT) TVs over the past 10 to 20 years.”

Dr Lei Xu, a team member from Nottingham Trent University, said: “There is significant room for further improvements by employing artificial intelligence and machine learning techniques to design and realise even smaller, thinner and more efficient metasurface displays.”

For more information about this research, please contact connect@tmos.org.au

* CMOS stands for Complementary Metal–Oxide–Semiconductor and is a technology used for constructing integrated circuit (IC) chips, including microprocessors, microcontrollers, memory chips, and other digital logic circuits. CMOS technology is also used for analog circuits such as image sensors (CMOS sensors), data converters, RF circuits (RF CMOS), and highly integrated transceivers for many types of communication.

Electrically programmable solid-state metasurfaces via flash localised heating

Khosro Zangeneh Kamali, Lei Xu, Nikita Gagrani, Hark Hoe Tan, Chennupati Jagadish, Andrey Miroshnichenko, Dragomir Neshev & Mohsen Rahmani

Light: Science & Applications, 22nd February 2023

In the last decades, metasurfaces have attracted much attention because of their extraordinary light-scattering properties. However, their inherently static geometry is an obstacle to many applications where dynamic tunability in their optical behaviour is required. Currently, there is a quest to enable dynamic tuning of metasurface properties, particularly with fast tuning rate, large modulation by small electrical signals, solid state and programmable across multiple pixels. Here, we demonstrate electrically tunable metasurfaces driven by thermo-optic effect and flash-heating in silicon. We show a 9-fold change in transmission by <5 V biasing voltage and the modulation rise-time of <625 µs. Our device consists of a silicon hole array metasurface encapsulated by transparent conducting oxide as a localised heater. It allows for video frame rate optical switching over multiple pixels that can be electrically programmed. Some of the advantages of the proposed tuning method compared with other methods are the possibility to apply it for modulation in the visible and near-infrared region, large modulation depth, working at transmission regime, exhibiting low optical loss, low input voltage requirement, and operating with higher than video-rate switching speed. The device is furthermore compatible with modern electronic display technologies and could be ideal for personal electronic devices such as flat displays, virtual reality holography and light detection and ranging, where fast, solid-state and transparent optical switches are required.