PMOS
The abbreviation PMOS (or PMOSFET and p-channel MOSFET) stands for “ p-type metal-oxide semiconductor ” (German: p-channel metal-oxide semiconductor ) and in microelectronics refers to a metal-oxide semiconductor -Field effect transistor (MOSFET), in which positively charged charge carriers (holes, defect electrons ) take over the conduction of the electric current in the channel . Circuits that only use p-channel MOSFETs as transistors in addition to resistors are known as PMOS logic. It is the complement to NMOS logic ( n-channel metal-oxide-semiconductor ), which uses electrons to conduct the electrical current in the channel. Circuits of both types have been and are manufactured using the so-called silicon gate technology (also known as the PMOS process).
technology
The dominant type of charge carrier , on whose movement the conductivity is based, is called the majority charge carrier . The majority charge carriers in PMOSFET are holes, also called defect electrons . With the NMOSFET it is electrons. As a result, the transistor channel of an enhancement-type PMOSFET consists of an n -doped semiconductor material and a depletion-type PMOSFET consists of a p-doped semiconductor material .
Since holes in silicon have about three times less effective charge carrier mobility than electrons, PMOS transistors in silicon have a switching speed that is approximately this factor lower than NMOS transistors with the same dimensions. The circuits that only use PMOS transistors are also summarized under the term PMOS technology. Although PMOS circuits were initially easier to manufacture, this disadvantage caused them to be replaced by NMOS technology in the mid-1970s.
Since the active transistors work with a passive load resistor in both pure PMOS technology and pure NMOS technology , a current flows during normal operation, which causes a not insignificant power requirement for the overall circuit. This can be significantly reduced if the load resistances are replaced by active, switched transistors of the respective complementary technology. This is implemented in today's dominant CMOS technology ( complementary metal-oxide-semiconductor , German complementary metal-oxide-semiconductor ), a circuit combination of PMOS and NMOS transistors.
Since the PMOS and NMOS transistors should have similar electrical properties for joint use in a CMOS circuit, the PMOS transistors are usually dimensioned differently, for example they have a larger transistor width. In modern circuits, PMOS transistors have even more differences to NMOS transistors: the charge carrier mobility is increased by tensioning the channel material (see stretched silicon ) or the gate structure is optimized for each type of transistor (material, doping, etc.). The latter has gained in importance, especially with the introduction of high-k + metal gate technology .
Applications
PMOS technology was the first economically producible MOS IC technology. For example, the Intel 4004 , the first microprocessor to be mass-produced, was manufactured using PMOS technology. Many products were later made functionally compatible using the faster NMOS technology. Examples of this are UARTs , keyboard controllers or the SC / MP microprocessor from National Semiconductor . Because of the low manufacturing costs, PMOS products could be used for a long time in applications such as pocket calculators , remote controls or clock circuits, which did not depend on higher speed or low power consumption.
Individual evidence
- ↑ Frank Kesel, Ruben Bartholomä: Design of digital circuits and systems with HDLs and FPGAs . Oldenbourg Verlag, 2006, ISBN 978-3-486-57556-9 , pp. 3, 131-132 .
- ↑ cf. Wadhwa: Microprocessor 8085: Architecture, Programming, and Interfacing . PHI Learning Pvt. Ltd., 2010, ISBN 978-81-203-4013-8 , pp. 9 ( limited preview in Google Book search).