Silicon on sapphire (SOS) is a hetero-epitaxial process for metal-oxide-semiconductor (MOS)

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

(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 ...

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 Uni ...

) 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 "sa ...

(Al₂O₃) 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, to reduce parasitic capacitance within the device, thereby improving perfo ...

(SOI) family of

CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSF ...

(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 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 conductors—conduct electric current ...

, 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 ha ...

, 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. Whe ...

, 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 Autonetics was a division of North American Aviation that produced various avionics but is best known for their inertial navigation systems used in submarines and intercontinental ballistic missiles. Its 188-acre facility in Anaheim, California, ...

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

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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 distinct ...

applications because of its inherent resistance to radiation. More recently, patented advancements in SOS processing and design have been made by

Peregrine Semiconductor Peregrine Semiconductor, known as pSemi, is a San Diego-based manufacturer of high-performance RF (radio frequency) CMOS integrated circuits. A Murata Manufacturing company since December 2014, the company's products are used in aerospace and defe ...

, 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.

has used SOS technology to develop RF integrated circuits (RFICs) including RF switches,

digital step attenuator Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals **Digital camera, which captures and stores digital i ...

s (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 depending on a control voltage (often abbreviated CV). VCAs have many applications, including audio level compression, synthesizers and ...

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 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 indus ...

markets.

Hewlett-Packard The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...

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, a ...

designs, particularly in the

HP 3000 The HP 3000 series is a family of 16-bit and 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, features that had mostly been limite ...

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 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