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Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact.^[1] The term is a portmanteau of the words static and friction,^[2] perhaps also influenced by the verb stick.

Any solid objects pressing against each other (but not sliding) will require some threshold of force parallel to the surface of contact in order to overcome static cohesion. Stiction is a threshold, not a continuous force.

In situations where two surfaces with areas below the micrometer scale come into close proximity (as in an accelerometer), they may adhere together. At this scale, electrostatic and/or Van der Waals and hydrogen bonding forces become significant. The phenomenon of two such surfaces being adhered together in this manner is also called stiction. Stiction may be related to hydrogen bonding or residual contamination.

Automobiles

Stiction is also the same threshold at which a rolling object would begin to slide over a surface rather than rolling at the expected rate (and in the case of a wheel, in the expected direction). In this case, it's called "rolling friction" or μ_r.

This is why driver training courses teach that if a car begins to slide sideways, the driver should try to steer in the same direction as the slide with no brakes. It gives the wheels a chance to regain static contact by rolling, which gives the driver some control again. An overenthusiastic driver may "squeal" the driving wheels trying to get a rapid start but this impressive display of noise and smoke is less effective than maintaining static contact with the road. Many stunt-driving techniques are also done by deliberately breaking and/or regaining this rolling friction.

A car on a slippery surface can slide a long way if the driver "locks" the wheels in stationary positions by pressing hard on the brakes. Anti-lock braking systems use wheel speed sensors and vehicle speed sensors to determine if any of the wheels have stopped turning. The ABS Module then briefly releases pressure to that wheel to allow the wheel to begin turning again. Anti-lock brakes can be much more effective than cadence braking which is essentially a non-automatic technique for doing the same thing.

Examples

Technik

Stiction refers to the characteristic of stop and start type motion as a force overcomes static friction and causes a part to accelerate under dynamic friction, but the force cannot keep up with the speed of the moving part so the part tends to stop again until the force catches up, and it happens repeatedly. Stiction is a problem for the design and materials science of many moving linkages. This is particularly the case for linear sliding joints, rather than rotating pivots. Owing to simple geometry, the moving distance of a sliding joint in two comparable linkages is longer than the circumferential travel of a pivoting bearing, thus the forces involved (for equivalent work) are lower and stiction forces become proportionally more significant. This issue has often led to linkages being redesigned from sliding to purely pivoted structures, just to avoid problems with stiction. An example is the Chapman strut, a suspension linkage developed by Colin Chapman of Lotus cars.^[3]

Surface micromachining

Stiction or adhesion between the substrate (usually silicon based) and the microstructure occurs during the isotropic wet etching of the sacrificial layer. The capillary forces due to the surface tension of the liquid between the microstructure and substrate during drying of the wet etchant cause the two surfaces to adhere together. Separating the two surfaces is often complicated due to the fragile nature of the microstructure. Stiction is often circumvented by the use of a sublimating fluid (often supercritical CO₂, which has extremely low surface tension) drying process where the liquid phase is bypassed. CO₂ displaces the rinsing fluid and is heated past the supercritical point. As the chamber pressure is slowly released the CO₂ sublimates thereby preventing stiction.

Digital storage tapes

Stiction may also manifest itself on computer tapes (9 track tape etc.). The magnetic surface of the tape would be heated against the read head in the tape deck, and when the tape stopped moving would cool slightly and "glue" onto the read head. This could be avoided by configuring the software so that the tape could be read continuously.^[4]

References

^ "Stiction, n." The Free Dictionary. Retrieved 23 May 2012.
^ "Stiction". Merriam-Webster. Retrieved 23 May 2012.
^ Ludvigsen, Karl (2010). Colin Chapman: Inside the Innovator. Haynes Publishing. p. 121. ISBN 978-1-84425-413-2.
^ Discussion by data recovery firm

[1] "Stiction, n." The Free Dictionary. Retrieved 23 May 2012.

[2] "Stiction". Merriam-Webster. Retrieved 23 May 2012.

[Ludvigsen,_Colin_Chapman-3] Ludvigsen, Karl (2010). Colin Chapman: Inside the Innovator. Haynes Publishing. p. 121. ISBN 978-1-84425-413-2.

[4] Discussion by data recovery firm

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 Stiction or adhesion between the [[Substrate (materials science)|substrate]] (usually [[silicon]] based) and the microstructure occurs during the isotropic [[etching (microfabrication)|wet etching]] of the sacrificial layer. The [[capillary action|capillary forces]] due to the [[surface tension]] of the liquid between the microstructure and substrate during drying of the wet etchant cause the two surfaces to [[Adhesion|adhere]] together. Separating the two surfaces is often complicated due to the fragile nature of the microstructure. Stiction is often circumvented by the use of a [[Sublimation (chemistry)|sublimating]] fluid (often [[supercritical carbon dioxide|supercritical]] CO<sub>2</sub>, which has extremely low surface tension) drying process where the liquid phase is bypassed. CO<sub>2</sub> displaces the rinsing fluid and is heated past the supercritical point. As the chamber pressure is slowly released the CO<sub>2</sub> sublimates thereby preventing stiction.
-===Hard disk drives===
-In the context of [[hard disk]] drives, stiction refers to the tendency of [[Disk read-and-write head|read/write heads]] to stick to the [[Hard disk platter|platters]]. Stiction is a result of smoothness and is exacerbated by humidity and other liquids condensing at the head-disk interface. Once the heads have stuck to the platters, the disk can be prevented from spinning up and can cause physical damage to the media and the slider. Other forces considered as responsible for stiction include electrostatic forces.{{Citation needed|date=April 2008}}
-In the early models of hard disk drives, stiction was known to cause read/write heads to stick to the platters of the hard drive due to the breakdown of lubricants used to coat the platters. During the late 1980s and early 1990s, as the size of hard drive platters decreased from the older 8" and 5.25" sizes to 3.5" and smaller, manufacturers continued to use the same calendering processes and lubricants used on the older, larger drives. The much tighter space caused much higher internal operating temperatures in these newer smaller drives, often leading to an accelerated breakdown of the surface lubricants into their much stickier components. When the drive was powered off and would cool down (for example at the end of the day when a user went home and shut off their PC), these now-broken-down lubricants would become quite viscous and sticky, sometimes causing the read/write heads to literally stick to the platter. One response to this problem was to remove the affected drive and strike it gently but firmly on the side, then try to start it while connected to but not necessarily fitted inside the machine. This might break the heads free for long enough to spin up the drive and recover the data from it without powering it down. Once started, it would continue to run indefinitely, but might not start again if powered down. Instead of tapping the drive, rotating it sharply by hand could start it. In most Maxtor hard drives, if the heads are stuck to the platters, the drive might make "music" from either the heads trying to move or from the platters trying to spin up.
-Modern hard drives have mostly solved the stiction problem by using [[Hard disk drive failure#Landing zones and load/unload technology|ramps]] to "unload" the heads from the disk surface on power-down. These ramps ensure the heads are not touching the platters, which not only prevents stiction but also keeps abrasion from kicking up microscopic particulates that can later contaminate the drive mechanism. Parking the heads in this manner also allows the voice coil actuator to be shut down to save power, so the heads are also frequently unloaded when the drive is idle. A competing solution is based on [[Hard disk drive failure#Landing zones and load/unload technology|laser textured landing zones]] near the ID of the platter where no data are stored. The heads are parked in that zone, and the actuator is latched until the next start-up. The landing zone consists of a controlled array of nanometer-level 'bumps' on the disk surface produced during manufacturing of the disk using a local substrate melting process employing suitable laser-based equipment. The method was pioneered by IBM around 1995 and is still widely in use in most desktop and server class HDDs.<ref>[http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=490199 A new laser texturing technique for high performance magnetic disk drives], Baumgart, P.; Krajnovich, D.J.; Nguyen, T.A.; Tam, A.G.; IEEE Trans. Magn.</ref>
 ===Digital storage tapes===