(Invited) Thin Film Technologies : The Key Approach for the Decrease of Energy Consumption of the Digital World

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Since the early 2000s, thanks to the parallel development of microelectronic tools and equipment, the increased possibility of nomadizing objects and improved transmission techniques, digital technologies have gradually invaded our 21st century world. The Internet of Things (IoT) and the Internet of Everything (IoE), based on connected objects, apply just as much to industry, online purchasing, leisure, finance and administration. All sectors of society are impacted, from communications, transport and energy, to health, the environment, security and industrial production (Industry 4.0).This field has experienced exponential growth since 2005, accelerating with the arrival of new application sectors such as social networks that concern the global population, cloud storage, crypto-currencies, 5G-6G, and especially artificial intelligence (AI) in recent years. All these new applicative domains are physically based on hardware that is constitued of electronic components and systems realized with microelectronic or even nanoelectronic elementary devices, integrated components and circuits, and large-area components including all display, signal sensor, actuators, and energy conversion devices. All this equipment needs to be supplied with electrical power in order to operate in a system that is essentially remote from the individual user.Thus, transparency on the user side of this digital world overshadows the fact that the associated energy consumption is also growing exponentially, despite improvements in microelectronics products that are therefore not yet sufficient. As exponential variation is not physically acceptable in the long term, we could in fact find ourselves in a global energy impasse over the next decade, as the electrical power required for digital technology becomes greater than the electrical power currently produced worldwide. Today's challenge is to reduce the energy consumption of all electronic systems, whether analog or digital, high-power, high-frequency and highly integrated. This approach must combine very large-scale integration and thin-film technologies, with new thin-film transistor architecture and/or devices based on new materials. After summarizing the context of the digital world and its challenges, this presentation examines the various proposals for improving electronics, both technologically and architecturally, involving transistors, devices and thin-film circuits. Indeed, new three-dimensional approaches combine highly integrated circuit techniques with thin-film technologies based on successive stacking of component layers. This technological architecture makes it possible to reduce the length of interconnection tracks, thereby improving signal transfer times and reducing resistive losses.The introduction of new materials such as metal oxide semiconductors, indium gallium zinc oxide (IGZO), or wide-bandgap semiconductors such as gallium nitride (GaN) or silicon carbide (SiC), can significantly reduce leakage currents in electronic components. These materials can be used in new semiconductor-on-insulator processes, extending the silicon-on-insulator approach. Indeed, the smart-cut technique applied to these wide-bandgap semiconductors can significantly reduce transistor leakage current and improve electrical characteristics such as breakdown voltage, on-resistance and cut-off frequency. This technique also allows reducing the power consumption of optolectronics devices. In addition, the use of a high permittivity insulator significantly decrease the off-state power consumption of each transistor, resulting in an energy efficiency improvement factor of up to ten.The recent development of integrated architectures based on flexible materials for large-area electronics paves the way for relatively low-power electronics. Indeed, a thin layer of indium gallium zinc oxide (IGZO) has been deposited on a flexible substrate, enabling the creation of a first-generation microprocessor (Intel 4004). In this circuit, IGZO-based transistors have a very high Ion/Ioff ratio which significantly minimizes leakage current and therefore power consumption. When the frequency performances do not limit the application, this type of circuit can be easily introduced in connected objects. Efforts on technological processes and new thin-film materials are complemented by new circuit and electrical system architectures. They should lead to an evolution of circuit architecture from a synchronous approach to an asynchronous and analog approach, which fortunately allows better control of energy consumption. For example, the introduction of a deep standby mode, generally used in case of inactivity, can considerably reduce losses and power dissipation.All these improvements can only be effective if future employees in the sector are capable of innovating. This challenge complements those of a technical nature. Indeed, globally, the electronics sector is experiencing a growing skills shortage, with many jobs going unfilled. There is an urgent need to train new engineers, technicians and doctors to increase the pool of specialists in the field, with training based on the knowledge and know-how of thin film technologies. The last part of the presentation is devoted to this issue and to the actions carried out by the French national network of higher education in microelectronics as part of a national France 2030 program.