+44 (0)24 7671 8970
More publications     •     Advertise with us     •     Contact us
Technical Insight

Magazine Feature
This article was originally featured in the edition:
Volume 30 Issue 2

Ga₂O₃ ICs offer exceptional promise for extreme environments


Fabricating logic circuits and flash memory highlights the potential of Ga2O3 ICs for serving in extreme environments.


Most computers have a relatively easy life. Whether in the form of a desktop, a laptop or a mobile device, they don’t tend to suffer from severe heat or cold, they don’t take much physical punishment, and thanks to the Earth’s magnetic fields, they are not bombarded by radiation.

But that’s not the case for all computers. Some have to endure extreme environments, including the likes of extreme cold, intense heat, electrical storms and high-energy radiation. For example, when computers are deployed in space missions, such as interplanetary space exploration, they are subjected to extreme temperatures and intense levels of radiation. High levels of radiation are also found in terrestrial nuclear reactors, while temperatures extremes are present at geothermal sites and in cryo electronics, a promising option for quantum computing.

At the heart of every computer are electronic ICs, which, when operating in extreme environments, have to function flawlessly under the likes of electrical storms, temperatures close to absolute zero and intense radiation. As these conditions threaten to damage and eventually degrade the IC, it is critical to develop electronics specifically designed to excel in these challenging environments.

For computers that operate in extreme environments, the two most important scenarios to consider are a high level of radiation and extreme temperatures. Each presents their own set of challenges and opportunities.

Table 1. Working conditions of electronics in extreme environments.

Let’s begin by considering radiation. This damages electronic systems through energetic particles and strong electromagnetic fields, creating issues that include resets, failures, signal glitches, noise, physical damage, and system shutdown. One of the drawbacks of most of today’s space electronics, which is based on silicon, is that it can only handle radiation up to 5 krad without damage. So, to operate in conditions where radiation is stronger, electronics are covered by heavy radiation-protecting shielding. However, even with this shielding, electronics degrades over time, reducing functionality and thus the lifetime of the space mission. For instance, the expected lifetime of satellites with silicon electronics is just 3 to 5 years, while the requirement for those in a geostationary orbit is much longer, typically 10 to 20 years. Due to this, solutions are needed to improve radiation tolerance in various digital and mixed-signal electronics, including ASICs and FPGAs, as well as complex heterogeneous integration microsystems.

Table 2. Physical properties of silicon, GaN, 4H-SiC, and Ga2O3 for applications in extreme environments.

In terms of temperature, standard silicon electronics is quite limited, with reliable operation possible between -40 °C to 150 °C. This is a major concern in a variety of applications. In oil and gas drilling, petrochemical applications and hypersonic vehicles, temperatures can reach up to 400 °C. In space, temperatures can be even higher – the surface of Venus is 460 °C – but in outer space is can be as low as −271 °C, so the electronics on board both space satellites and rovers has to operate over a very wide temperature range. To ensure optimal system performance, it is crucial that sensors, communications systems and control circuitry function effectively under these extreme temperatures.

Note that not all extreme conditions come from external factors; high power can stress microelectronics and their surroundings. Due to this, it is essential to develop new devices that are capable of managing high voltages, high currents and high powers, as well as advanced insulating materials and low-loss passive components. This approach is necessary to ensure the reliability and functionality of electronic systems operating in challenging environments.

Computing and material requirements

The use of computing chips in extreme environments is characterised by a greater variety of applications and heavy workloads. Specifically, in applications such as space exploration, the geothermal and petrochemical industries, as well as quantum computing, there is often the requirement for computers to be rugged, light, compact, and energy efficient. In addition, these computers must be capable of withstanding extreme conditions, such as low and high temperatures and strong radiation (see Table 1), ideally without having to draw on a heavy and bulky payload for temperature management and radiation shielding.

Figure 1. A Ga2O3 DCFL inverter (a) cross-sectional diagram. (b) An optical microscope image of the DCFL circuit.

For any electronic IC chip, the basic underlying technology is based on semiconductor materials capable of offering insulating and conducting properties, when subjected to an external electrical or optical ‘bias’. To build robust computing chips, ideally these materials can endure extreme environments. That means that as well as resisting melting, these materials are capable of withstanding potential failures caused by thermal or mechanical stress. In addition, they need to remain stable, avoiding degradation due to changes in their structure caused by heat, or surface damage resulting from the likes of diffusion, oxidation, vaporisation or ablation.

A number of elemental and compound semiconductor materials have been explored over the years, with efforts motivated by understanding their properties and determining their capability for producing various devices. Amongst them, silicon serves as the foundational source for all electronic innovations that exist in our daily lives. It is abundant and scalable, with a high mobility for electrons and holes, but due its narrow bandgap, its usage is constrained in harsh environmental conditions.

Two materials with a wider bandgap, GaN and SiC, provide a better performance, in terms of high temperature capability and radiation tolerance. However, both offer limited performance at low temperatures, with carriers in both bulk materials freezing out below 40K. (Note, though, that GaN transistors based on a polarisation-induced carrier gas are not sensitive to low temperature.) Additionally, GaN and SiC lack native oxides, potentially resulting in less stable IC operation in extreme environments. For instance, a single event burnout due to heavy ion damage is a big issue for SiC MOSFETs.

Figure 2. Ga2O3 dual-stage inverter circuits. (a) pseudo-R, (b) pseudo-E, and (c) pseudo-D schematics. Fabricated devices with transconductance ratio, KR, of 1. (d) pseudo-R. (e) pseudo-E. (f) pseudo-D. Fabricated devices with a KR of 28.8. (g) pseudo-R. (h) pseudo-E. (i) pseudo-D.

A far more attractive candidate may be Ga2O3. As well as being blessed with a larger bandgap than GaN and SiC, it offers well-balanced properties, and there are no significant drawbacks that might hinder its performance (see Table 2, which highlights the physical properties of silicon, GaN, 4H-SiC, and Ga2O3 for applications in extreme environments).

Ga2O3 is a great allrounder, offering superior properties in all extreme environmental conditions, including low and high temperatures and high levels of radiation, while maintaining a decent mobility. Another important attribute of Ga2O3 is that native bulk substrates can be produced at a lower cost than GaN and SiC substrates, crucial for low cost and scalability of ICs, thanks to the opportunity to use low-cost melt-grown techniques. Further improvement of heteroepitaxial Ga2O3 could further lower the cost significantly.

Blessed with an ultra-wide bandgap and extensive electron doping capabilities, Ga2O3 provides a promising solution for handling high powers – high-voltage and large-current electronics, as well as extreme temperature applications. During the last decade or so, Ga2O3-based transistors and Schottky diodes have been extensively studied, yielding impressive results that include a voltage handling capacity of around 8 kV and operational temperatures of up to 500 °C.

However, to operate in extreme environmental conditions, there is a need for electronic systems, which process and store information, to incorporate vital electronic components – specifically, logic circuits and flash memory built on Ga2O3.

Our team from King Abdullah University of Science and Technology (KAUST) is embarking on this challenge, and has already taken strides towards developing an advanced computing and memory chip that operates reliably in extreme temperatures. Breaking new ground, we have demonstrated the functionality of logic and memory components using heteroepitaxial β-Ga2O3, grown on a sapphire substrate. This triumph takes us closer to realising highly dependable, efficient, and compact computing systems designed to withstand extreme conditions.