A recent article in IEEE Spectrum highlighted a recently discovered weakness in some prominent electronic controls. In the late 1990’s, IC manufacturers began to use MOS-FET technology as the basis for their integrated circuits. This remains the dominate technology today.
A simple explanation of the MOS-FET transistor may be helpful. (MOS-FET is an acronym for Metallic Oxide Semiconductor-Field Effect Transistor) A MOS-FET transistor is composed of a channel, through which current can flow; and a gate which controls the flow of current by imposing an electric field around the channel.
It is common knowledge that some electronic components deteriorate with age. For example, capacitors can begin to break down and leak as they get old. Some resistors can become brittle with age and crack. But now it has been discovered that the MOS- FET also has an aging problem. As passive components such as resistors and capacitors age they may cause the overall system to slow down or become unstable. But when an active component like a transistor or IC fails, the system fails. It has been discovered that MOS-FETs, over time (about 20 years or so), begin to experience current leakage in the channel. In other words, the gate can no longer turn off the current flow sufficiently. (To be accurate, there is always some small leakage current in a MOS-FET but the system design takes this into consideration). This condition can result in many different consequences: erratic operation, nuisance shut downs, sensitivity to electromagnetic interference and many more.
The conclusion we draw from this is that, electronic control systems may not be as immortal as we once thought. This, coupled with the fact that control system manufacturers cease to provide replacement parts after about ten years, makes it prudent to plan for the eventual control system obsolescence. Planning ahead for the cost and downtime associated with a control system upgrade can minimize the shock of this eventual necessity.