Leakage (semiconductors)
Encyclopedia
In semiconductor device
s, leakage is a quantum phenomenon where mobile charge carriers (electrons or holes
) tunnel through an insulating region. Leakage increases exponentially as the thickness of the insulating region decreases. Tunneling leakage can also occur across semiconductor junctions between heavily doped P-type
and N-type semiconductor
s. Other than tunneling via the gate insulator
or junctions, carriers can also leak between source and drain terminals of a Metal Oxide Semiconductor (MOS) transistor
. This is called subthreshold conduction. The primary source of leakage occurs inside transistor
s, but electrons can also leak between interconnects. Leakage increases power consumption and if sufficiently large can cause complete circuit failure.
Leakage is currently one of the main factors limiting increased computer processor performance. Efforts to minimize leakage include the use of strained silicon
, high-k dielectric
s, and/or stronger dopant
levels in the semiconductor. Leakage reduction to continue Moore's law
will not only require new material solutions but also proper system design.
Certain types of semiconductor manufacturing defects exhibit themselves as increased leakage. Thus measuring leakage, or Iddq testing
, is a quick, inexpensive method finding defective chips.
Increased leakage is a common failure mode
resulting from non-catastrophic overstress of a semiconductor device, when the junction or the gate oxide suffers permanent damage not sufficient to cause a catastrophic failure
. Overstressing the gate oxide can lead to stress-induced leakage current
.
In bipolar junction transistor
s, the emitter current is sum of the collector and base currents. Ie = Ic + Ib. The collector current has two components, minority carriers and majority carriers. The minority current is called the leakage current.
Leakage current is generally measured in microamperes. For a reverse-biased diode it is temperature sensitive. Leakage current must be carefully examined for applications that work in wide temperature ranges.
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...
s, leakage is a quantum phenomenon where mobile charge carriers (electrons or holes
Electron hole
An electron hole is the conceptual and mathematical opposite of an electron, useful in the study of physics, chemistry, and electrical engineering. The concept describes the lack of an electron at a position where one could exist in an atom or atomic lattice...
) tunnel through an insulating region. Leakage increases exponentially as the thickness of the insulating region decreases. Tunneling leakage can also occur across semiconductor junctions between heavily doped P-type
P-type semiconductor
A P-type semiconductor is obtained by carrying out a process of doping: that is, adding a certain type of atoms to the semiconductor in order to increase the number of free charge carriers ....
and N-type semiconductor
N-type semiconductor
N-type semiconductors are a type of extrinsic semiconductor where the dopant atoms are capable of providing extra conduction electrons to the host material . This creates an excess of negative electron charge carriers....
s. Other than tunneling via the gate insulator
Gate oxide
The gate oxide is the dielectric layer that separates the gate terminal of a MOSFET from the underlying source and drain terminals as well as the conductive channel that connects source and drain when the transistor is turned on. Gate oxide is formed by oxidizing the silicon of the channel to form...
or junctions, carriers can also leak between source and drain terminals of a Metal Oxide Semiconductor (MOS) transistor
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
. This is called subthreshold conduction. The primary source of leakage occurs inside transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s, but electrons can also leak between interconnects. Leakage increases power consumption and if sufficiently large can cause complete circuit failure.
Leakage is currently one of the main factors limiting increased computer processor performance. Efforts to minimize leakage include the use of strained silicon
Strained silicon
Strained silicon is a layer of silicon in which the silicon atoms are stretched beyond their normal interatomic distance. This can be accomplished by putting the layer of silicon over a substrate of silicon germanium...
, high-k dielectric
High-k Dielectric
The term high-κ dielectric refers to a material with a high dielectric constant κ used in semiconductor manufacturing processes which replaces the silicon dioxide gate dielectric...
s, and/or stronger dopant
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
levels in the semiconductor. Leakage reduction to continue Moore's law
Moore's Law
Moore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
will not only require new material solutions but also proper system design.
Certain types of semiconductor manufacturing defects exhibit themselves as increased leakage. Thus measuring leakage, or Iddq testing
Iddq testing
Iddq testing is a method for testing CMOS integrated circuits for the presence of manufacturing faults. It relies on measuring the supply current in the quiescent state...
, is a quick, inexpensive method finding defective chips.
Increased leakage is a common failure mode
Failure modes of electronics
Electronic components have a wide range of failure modes. These can be classified in various ways, such as by time or cause. Failures can be caused by excess temperature, excess current or voltage, ionizing radiation, mechanical shock, stress or impact, and many other causes...
resulting from non-catastrophic overstress of a semiconductor device, when the junction or the gate oxide suffers permanent damage not sufficient to cause a catastrophic failure
Catastrophic failure
A catastrophic failure is a sudden and total failure of some system from which recovery is impossible. Catastrophic failures often lead to cascading systems failure....
. Overstressing the gate oxide can lead to stress-induced leakage current
SILC (semiconductors)
Stress Induced Leakage Current is an increase in the gate leakage current of a MOSFET, due to defects created in the gate oxide during electrical stressing. SILC is perhaps the largest factor inhibiting device miniaturization...
.
In bipolar junction transistor
Bipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
s, the emitter current is sum of the collector and base currents. Ie = Ic + Ib. The collector current has two components, minority carriers and majority carriers. The minority current is called the leakage current.
Leakage current is generally measured in microamperes. For a reverse-biased diode it is temperature sensitive. Leakage current must be carefully examined for applications that work in wide temperature ranges.