What is Fully depleted Silicon on Insulator (FD-SOI)?
François Andrieu : The FD-SOI technology was born forty years ago in the heart of the French Alps, in Grenoble, in the laboratories of CEA-Leti. FD-SOI is used for transistors, the key electronic component which modulates or amplifies electrical currents. The revolutionary idea of CEA-Leti’s engineers was to develop it not from a block of solid silicon, but rather from an ultra-thin silicon wafer on an oxide insulating layer. These electronic components are today etched on silicon wafers, which take the form of ultra-thin circular disks 300 mm in diameter. They are sold worldwide by French company SOITEC, the world leader in SOI wafers, which is a 90s spin-off from CEA-Leti. Samsung and GlobalFoundries both sell FD-SOI components.
Placed on an insulating layer, components on an ultra-thin film are intrinsically immunized against current leakage. FD-SOI is 25% faster than equivalent transistors on solid silicon, and consumes up to 40% less energy, particularly thanks to leakage control. Today, it is experiencing a new lease of life with the search for energy frugality for the Internet of Things (IoT) and the needs of 5G+ mobile phones. It’s made a strong fightback, keeping in mind that opinions about it were long divided in the small world of microelectronics. Its story is far from over; FD-SOI has the potential to achieve engraving sizes below 10 nanometers.
Where is FD-SOI found ?
• Microcontrollers : Processors that make calculations, manage, and make decisions.
• Connected speakers
• Voice control switches
• Car radars
• 5G smartphone
How would you explain the success of FD-SOI chips made in France in smartphones?
Eric Mercier : Used up to now for its low energy consumption assets in IoT devices and microcontrollers, " FD-SOI" CMOS (Complementary Metal Oxide Semiconductor) transistor technology now appeals to mobile phone manufacturers for its radiofrequency (RF) performance, particularly in millimeter-wave high frequencies.
FD-SOI meets 5G requirements, which are now and will in future be leveraging millimeter waves, located in frequency bands above 12 GHz. The antennae operating in these wave bands are small-sized, measuring only a few millimeters, because the wavelengths are short, which makes them highly directive when assembled in a compact network. This directivity makes it possible to increase the effective link between the emitter and the receiver, by maximizing power output. In this kind of antenna network, the overall emitted power corresponds to the sum of the individual powers of each network element, consequently requiring less power, in the range of several dozen milliwatts, which can therefore be associated with an integrated circuit made using FD-SOI technology.
What are the advantages and benefits of FD-SOI technology for mobile telephony and the 5G network?
François Andrieu : With millimeter wave frequency bands, FD-SOI technology offers competitive solutions for several RF (radiofrequency) blocks, particularly power amplifiers and low noise amplifiers that constitute antenna networks. Additionally, its good energy efficiency makes it a technology of choice for 5G and future generations of broadband networks. FD-SOI transistors exhibit less parasitic capacitance than the competitor technology (FinFET), used worldwide in fast processors found in telephones and computers, allowing these devices to be operated at higher frequency with better energy efficiency. Above all, this technology offers the ability to co-integrate these high-performance RF blocks with some of the most advanced analog and digital blocks (22 nm-18 nm) on the market in terms of miniaturization, all on the same chip. This makes the manufacturing process competitive and energy efficient.
Eric Mercier : In addition to its competitive performance levels, FD-SOI is proving to be less expensive than its competitor, FinFET, in terms of manufacturing radiofrequency emitters/receivers for 5G/6G systems that operate in the range of millimeter waves (RF front end module type applications). In fact, Google has adopted this technology for its 5G millimeter band emitter-receiver, which is equipping its new generation of Pixel 6 smartphones, launched in October 2021. This radiofrequency component is equipped with 28-nanometer FD-SOI technology made by Samsung licensed to STMicroelectronics.