Silicon on sapphire (SOS) is a hetero-epitaxial process for metal-oxide-semiconductor (MOS) integrated circuit (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 secondary sector of the economy. The term may refer to a ...

that consists of a thin layer (typically thinner than 0.6

µm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

) of

silicon Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ...

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, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sap ...

(Al₂O₃)

wafer A wafer is a crisp, often sweet, very thin, flat, light and dry biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. Wafers can also be made into cookies with cream flavoring sandwiched between them. They ...

. SOS is part of the silicon-on-insulator (SOI) family of CMOS (complementary MOS) technologies. Typically, high-purity artificially grown

crystals are used. The silicon is usually deposited by the decomposition of

silane Silane is an inorganic compound with chemical formula, . It is a colourless, pyrophoric, toxic gas with a sharp, repulsive smell, somewhat similar to that of acetic acid. Silane is of practical interest as a precursor to elemental silicon. Sila ...

gas (SiH₄) on heated sapphire substrates. The advantage of sapphire is that it is an excellent electrical insulator, 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 upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch ...

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 geometry and crystallography, a Bravais lattice, named after , is an infinite array of discrete points generated by a set of discrete translation operations described in three dimensional space by : \mathbf = n_1 \mathbf_1 + n_2 \mathbf_2 + n ...

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

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It h ...

, a p-type

dopant A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. Wh ...

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

History

In 1963,

Harold M. Manasevit Dr. Harold M. Manasevit (1927–2008) was an American materials scientist. Manasevit received a B.S. Degree in Chemistry from Ohio University in 1950, M.S. in Chemistry from Pennsylvania State University in 1951, and Ph.D. in Physical Inorganic C ...

was the first to document epitaxial growth of silicon on sapphire while working at the Autonetics division of

North American Aviation North American Aviation (NAA) was a major American aerospace manufacturer that designed and built several notable aircraft and spacecraft. Its products included: the T-6 Texan trainer, the P-51 Mustang fighter, the B-25 Mitchell bomber, the ...

(now

Boeing The Boeing Company () is an American multinational corporation that designs, manufactures, and sells airplanes, rotorcraft, rockets, satellites, telecommunications equipment, and missiles worldwide. The company also provides leasing and ...

). 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 at RCA Laboratories fabricated a

MOSFET The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...

(metal-oxide-semiconductor field-effect transistor) using the silicon-on-sapphire process. 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 astrona ...

and

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

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

Applications

Silicon on sapphire pressure transducer, pressure transmitter and temperature sensor diaphragms have been manufactured utilizing a patented process b
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 amplifier A variable-gain (VGA) or voltage-controlled amplifier (VCA) is an electronic amplifier that varies its Gain (electronics), gain depending on a control voltage (often abbreviated CV). VCAs have many applications, including audio level compression, ...

s. 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 markets. Hewlett-Packard used SOS in some of their

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

designs, particularly in the HP 3000 line of computers.

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 In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type ...

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