Silicon on sapphire (SOS) is a hetero-epitaxial process for

metal–oxide–semiconductor upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale. In electronics, the metal–oxide–semiconductor field- ...

(MOS)

integrated circuit An integrated circuit (IC), also known as a microchip or simply chip, is a set of electronic circuits, consisting of various electronic components (such as transistors, resistors, and capacitors) and their interconnections. These components a ...

(IC)

manufacturing Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of the secondary sector of the economy. The term may refer ...

that consists of a thin layer (typically thinner than 0.6 μm) of

silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...

grown on a

sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, cobalt, lead, chromium, vanadium, magnesium, boron, and silicon. The name ''sapphire ...

() wafer. SOS is part of the

silicon-on-insulator In semiconductor manufacturing, silicon on insulator (SOI) technology is fabrication of silicon semiconductor devices in a layered silicon–insulator–silicon substrate (materials science), substrate, to reduce parasitic capacitance within the d ...

(SOI) family of

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss ", , ) is a type of MOSFET, metal–oxide–semiconductor field-effect transistor (MOSFET) semiconductor device fabrication, fabrication process that uses complementary an ...

(complementary MOS) technologies. Typically, high-purity artificially grown sapphire crystals are used. The silicon is usually deposited by the decomposition of

silane Silane (Silicane) is an inorganic compound with chemical formula . It is a colorless, pyrophoric gas with a sharp, repulsive, pungent smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental ...

gas () on heated sapphire substrates. The advantage of sapphire is that it is an excellent

electrical insulator An electrical insulator is a material in which electric current does not flow freely. The atoms of the insulator have tightly bound electrons which cannot readily move. Other materials—semiconductors and electrical conductor, conductors—con ...

, preventing stray currents caused by radiation from spreading to nearby circuit elements. SOS faced early challenges in commercial manufacturing because of difficulties in fabricating the very small

transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...

s used in modern high-density applications. This is because the SOS process results in the formation of dislocations, twinning and stacking faults from

crystal lattice In crystallography, crystal structure is a description of ordered arrangement of atoms, ions, or molecules in a crystal, crystalline material. Ordered structures occur from intrinsic nature of constituent particles to form symmetric patterns that ...

disparities between the sapphire and silicon. Additionally, there is some

aluminum Aluminium (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...

, a p-type

dopant A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optics, optical properties. The amount of dopant is typically very low compared to the material b ...

, contamination from the substrate in the silicon closest to the interface.

History

In 1963, Harold M. Manasevit was the first to document epitaxial growth of silicon on sapphire while working at the Autonetics division of

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(now

Boeing The Boeing Company, or simply Boeing (), is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, and missiles worldwide. The company also provides leasing and product support s ...

). In 1964, he published his findings with colleague William Simpson in the ''Journal of Applied Physics''. In 1965, C.W. Mueller and P.H. Robinson fabricated a

MOSFET upright=1.3, Two power MOSFETs in amperes">A in the ''on'' state, dissipating up to about 100 watt">W and controlling a load of over 2000 W. A matchstick is pictured for scale. In electronics, the metal–oxide–semiconductor field- ...

(metal–oxide–semiconductor field-effect transistor) using the silicon-on-sapphire process at RCA Laboratories. SOS was first used in

aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial, and military applications. Aerospace engineering consists of aeronautics and astron ...

and

military A military, also known collectively as armed forces, is a heavily armed, highly organized force primarily intended for warfare. Militaries are typically authorized and maintained by a sovereign state, with their members identifiable by a d ...

applications because of its inherent resistance to radiation. More recently, patented advancements in SOS processing and design have been made by Peregrine Semiconductor, allowing SOS to be commercialized in high-volume for high-performance radio-frequency (RF) applications.

Circuits and systems

The advantages of the SOS technology allow research groups to fabricate a variety of SOS circuits and systems that benefit from the technology and advance the state-of-the-art in: * analog-to-digital converters (a nano-Watts prototype was produced by Yale e-Lab) * monolithic digital isolation buffers * SOS-CMOS image sensor arrays (one of the first standard CMOS image sensor arrays capable of transducing light simultaneously from both sides of the die was produced by Yale e-Lab) * patch-clamp amplifiers * energy harvesting devices * three-dimensional (3D) integration with no galvanic connections * charge pumps * temperature sensors * early microprocessors, such as the RCA 1802

Applications

Silicon on sapphire pressure transducer, pressure transmitter and temperature sensor diaphragms have been manufactured using a patented process by Armen Sahagen since 1985. Outstanding performance in high temperature environments helped propel this technology forward. This SOS technology has been licensed throughout the world. ESI Technology Ltd. in the UK have developed a wide range of pressure transducers and pressure transmitters that benefit from the outstanding features of silicon on sapphire. Peregrine Semiconductor has used SOS technology to develop RF integrated circuits (RFICs) including RF switches, digital step attenuators (DSAs), phase locked-loop (PLL) frequency synthesizers, prescalers, mixers/ upconverters, and variable-gain amplifiers. These RFICs are designed for commercial RF applications such as mobile handsets and cellular infrastructure, broadband consumer and DTV, test and measurement, and industrial public safety, as well as rad-hard

and

defense Defense or defence may refer to: Tactical, martial, and political acts or groups * Defense (military), forces primarily intended for warfare * Civil defense, the organizing of civilians to deal with emergencies or enemy attacks * Defense industr ...

markets.

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company. It was founded by Bill Hewlett and David Packard in 1939 in a one-car garage in Palo Alto, California ...

used SOS in some of their CPU designs, particularly in the

HP 3000 The HP 3000 series is a family of 16-bit computing, 16-bit and 32-bit computing, 32-bit minicomputers from Hewlett-Packard. It was designed to be the first minicomputer with full support for time-sharing in the hardware and the operating system, ...

line of computers. Silicon on sapphire chips produced in the 1970s proved superior in performance to their all silicon counterparts, but this came at the cost of lower yields of just 9%.

Substrate analysis: SOS structure

The application of epitaxial growth of silicon on sapphire substrates for fabricating MOS devices involves a silicon purification process that mitigates crystal defects which result from a mismatch between sapphire and silicon lattices. For example, Peregrine Semiconductor's SP4T switch is formed on an SOS substrate where the final thickness of silicon is approximately 95 nm. Silicon is recessed in regions outside the polysilicon gate stack by poly oxidation and further recessed by the sidewall spacer formation process to a thickness of approximately 78 nm.

History

Circuits and systems

Applications

Substrate analysis: SOS structure

See also

References

Further reading