Researchers at the National Institute of Standards and Technology (NIST) and collaborators have devised and tested a new, highly sensitive method of detecting and counting defects in transistors — a matter of urgent concern to the semiconductor industry as it develops new materials for next-generation devices. These defects limit transistor and circuit performance and can affect product reliability.
A typical transistor is, for most uses, basically a switch. When it’s on, current flows from one side of a semiconductor to the other; switching it off stops the current. Those actions respectively create the binary 1s and 0s of digital information.
Transistor performance critically depends on how reliably a designated amount of current will flow. Defects in the transistor material, such as unwanted “impurity” regions or broken chemical bonds, interrupt and destabilize the flow. These defects can manifest themselves immediately or over a period of time while the device is operating.
Over many years, scientists have found numerous ways to classify and minimize those effects.
During normal transistor operation, a conductive channel (controlled by the gate) forms between the source and drain, allowing a current to flow.
Credit: Sean Kelley/NIST
However, electrons moving from the source to the drain can encounter defects that lead to recombination with a hole, resulting in a loss of current and making the transistor unreliable. The most important of these are called interface defects, existing at the interface between the silicon oxide and silicon layers.
Credit: Sean Kelley/NIST
In order to count these defects, researchers place the transistor into “bipolar amplification” mode by applying a voltage to the source and gate. This creates a decreasing concentration of electrons across the channel. In this configuration, the current from the source t ..
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