![]() ![]() Scientists all but abandoned the technique. As transistor dimensions shrank, the tunneling current leaking through the insulating oxide layer made it nearly impossible to detect defects with ordinary charge pumping. The thinner the material, the higher the probability that electrons will escape, creating a tunneling current. The greater the output current, the larger the number of defects.Īccording to quantum theory, electrons and other subatomic particles can never be truly trapped there's always some probability they will escape or "tunnel" out of an enclosure or boundary layer. This activity generates a current proportional to the number of defects. The negative voltage also attracts positive charge carriers, known as "holes," to the region, where they combine with electrons trapped in the defects. In the second step, a negative voltage is applied, to rid the interface of the excess electrons, leaving only the trapped ones behind. Some of the pumped electrons become trapped in defects at the interface, but there are many electrons left over. In the first step of the test, the positive voltage attracts or pumps electrons, which are negatively charged, to the boundary or interface between the gate's insulating layer and the body of the transistor. (The transistor does not act as an on/off switch during this testing mode.) In traditional charge pumping, the alternating voltage pulses are applied at a single, set frequency. ![]() The gate controls the amount of current in the channel.Ĭharge pumping is a two-step process in which the examiner alternately pulses the gate with a positive test voltage, then a negative one. ![]() In a typical transistor, current travels through a narrow channel, only one billionth of a meter thick, that extends from the source, which lies on one side of the gate, to a "drain" on the other side. Below the insulating layer lies the interface region that separates the insulating layer and the main body of the semiconductor. In the traditional design known as the metal oxide semiconductor field effect transistor (MOSFET), a metal electrode called the gate sits atop a thin insulating layer of silicon dioxide. Scientists have devised several ways to categorize defects and minimize their impact, tailored to the structure of the transistor under study.Ĭredit: National Institute of Standards and Technology Or they could be atomic impurities that trap electrons in the material. These defects could be broken chemical bonds in the transistor material. In the off position, representing the "0" of binary logic, current ceases to flow.ĭefects in a transistor can interfere with the reliable flow of current and significantly degrade the performance of transistors. In the on position, which represents the "1" of binary digital information, a designated amount of current flows from one side of a semiconductor to the other. The ability to manipulate individual spins has applications in both basic research and quantum engineering and computing. ![]() Researchers could also use the new capability to detect and manipulate a property in each electron known as quantum spin. The new, modified charge pumping technique can detect single defects as small as the diameter of a hydrogen atom (one-tenth of a billionth of a meter) and can indicate where they're located in the transistor. ![]()
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