Transistor aging (sometimes called silicon aging) is the process 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 ta ...

transistors 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 ...

developing flaws over time as they are used, degrading performance and reliability, and eventually failing altogether. Despite the name, similar mechanisms may affect transistors made of any kind of semiconductor. Manufacturers compensate for this (as well as manufacturing defects) by running chips at slower speeds than they are initially capable of.

Causes

The main causes of transistor aging in MOSFETs are ''electromigration'' and ''charge trapping''. Electromigration is the movement of

ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...

s caused by momentum from the transfer of

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no ...

s in the conductor. This results in degradation of the material, causing intermittent glitches that are very difficult to diagnose, and eventual failure. Charge trapping is related to

time-dependent gate oxide breakdown Time-dependent gate oxide breakdown (or time-dependent dielectric breakdown, TDDB) is a kind of transistor aging, a failure mechanism in MOSFETs, when the gate oxide breaks down as a result of long-time application of relatively low electric field ...

, and manifests as an increase in resistance and

threshold voltage The threshold voltage, commonly abbreviated as Vth or VGS(th), of a field-effect transistor (FET) is the minimum gate-to-source voltage (VGS) that is needed to create a conducting path between the source and drain terminals. It is an important s ...

(the voltage needed for the transistor to conduct), and a decrease in drain current. This degrades the chip performance over time, until ultimately the thresholds collapse. Charge trapping occurs in several ways: * Hot carrier injection (HCI) is where electrons gain enough energy to leak into the oxide, becoming trapped there and possibly damaging it. * Random telegraph noise (RTN) can also result, where the drain current fluctuates between several discrete levels, and is worsened with increasing temperature. * Bias temperature instability (BTI) is where charge leaks into the oxide when voltage is applied to the gate, even with no current flowing through the transistor. When the voltage is removed from the gate, the charges gradually dissipate between milliseconds or hours. Charge trapping was determined by

John Szedon John is a common English name and surname: * John (given name) * John (surname) John may also refer to: New Testament Works * Gospel of John, a title often shortened to John * First Epistle of John, often shortened to 1 John * Second E ...

and Ting L. Chu to be a viable means of storing digital information, and was developed into the SONOS, MirrorBit, and 3D NAND flash memory technologies.

References

* *{{cite web , title=Silicon Aging and Signal Integrity , first=Alan , last=Sguigna , date=25 Aug 2013 , publisher=ASSET InterTech , url=https://blog.asset-intertech.com/test_data_out/2013/08/silicon-aging-and-signal-integrity.html , accessdate=21 Jun 2020 Transistors Semiconductor device defects

Causes

See also

References