Bicmos Technology - Overview

Brief intro about Bicmos

1. Bi-CMOS Technology

2. What is BiCMOS ? This is one of the major semiconductor technologies and is a highly developed technology In 1990s, two separate technologies were incorporated, namely bipolar junction transistor ( offering high speed and gain ) and CMOS  transistor  (excels for constructing simple, low-power logic gates ) in a single modern integrated circuit. BiCMOS is able to achieve VLSI circuits with speed-power-density performance previously unattainable with either technology individually.

3. VLSI Circuits Very-large-scale integration  ( VLSI ) is the process of creating an  integrated circuit  (IC) by combining billions of  transistors  into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. VLSI helped in integrating a   CPU, ROM, RAM  and other  glue logic into one chip . The   microprocessor  is a VLSI device.

4. A VLSI IC DIE Courtesy: Wikipedia (  GNU Free Documentation License )

5. What is CMOS ? CMOS is the abbreviated version of Complementary Metal – Oxide – Semiconductor (MOS). O ne of the most popular technology in the computer chip design industry and broadly used to form  integrated circuits . This is the dominant semiconductor technology for microprocessors, microcontroller chips, memories like RAM, ROM,  EEPROM and application  specific integrated circuits (ASICs).

6. NMOS NMOS is built on a p-type substrate with n-type source and drain diffused on it. In NMOS, the majority carriers are electrons. Therefore, much faster than PMOS. NMOS will conduct when high voltage is applied to the gate.

7. PMOS P- channel MOSFET consists P-type Source and Drain diffused on an N-type substrate. Majority carriers are holes. PMOS will conduct When a low voltage is applied to the gate. The PMOS devices are more immune to noise than NMOS devices.

8. CMOS realization as NAND GATE INPUT OUTPUT NMOS PMOS PMOS + NMOS =Output A B A B 1 1 1 1 1 1 1 1 1 1 1

9. What is BiPolar Technology ? Bipolar transistors are part of ICs and their operation is based on two types of semiconductor material, namely – n-type(excess of electrons) p-type(excess of holes) It is named Bipolar because its operation involves conduction by two carriers: electrons and holes in the same crystal . Also, BJT is a current controlled device.

10. NPN BJT Transistor The emitter is more Negative with base and also with respect to the collector.  Base is lightly doped with holes.

11. PNP BJT Transistor The emitter is more Positive with base and also with respect to the collector.  Base is lightly doped with electrons.

12. Construction (NPN) The bipolar junction transistor (NPN) three layer semiconductor sandwich with an  emitter  and  collector  at the ends, and a  base  in between. The key to the fabrication of a bipolar junction transistor is to make the middle layer, the base, as thin as possible without shorting the outside layers – the emitter and the collector . The Emitter is heavily doped with electrons, base is lightly doped with holes and collector is moderately doped with electrons.

13. Working(NPN) The transistor is in OFF state when the base voltage is same as the emitter voltage. The transistor mode is in ON state when the base voltage decreases with respect to the emitter . To Operate BJT in Active region, BE junction is made forward bias and the CB is made reverse bias junction.

14. Advantages of BiCMOS technology Analog amplifier design is facilitated and improved by using high impedance CMOS circuit as input and remaining are realized by using bipolar transistors. BiCMOS is essentially vigorous to temperature and process variations offering good economical considerations (high percentage of prime units) with less variability in electrical parameters. High load current sinking and sourcing can be provided by BiCMOS devices as per requirement. Since it is a grouping of bipolar and CMOS technologies we can use BJT if speed is a critical parameter and we can use MOS if power is a critical parameter and it can drive high capacitance loads with reduced cycle time.

15. It has low power dissipation than bipolar technology alone. This technology found frequent applications in analog power managing circuits and amplifier circuits such as BiCMOS amplifier. It is well appropriate for input/ ouput intensive applications, offers flexible inputs/outputs (TTL, CMOS and ECL). It has the advantage of improved speed performance compared to CMOS technology alone. Latch up invulnerability. It has the bidirectional capability (source and drain can be interchanged as per requirement).

16. Drawbacks of BiCMOS technology The fabrication process of this technology is comprised of both the CMOS and bipolar technologies increasing the complexity. Due to increase in the complexity of the fabrication process, the cost of fabrication also increases. As there are more devices, hence, less lithography.

17. BiCMOS technology and Applications It can be analyzed as AND function of high density and speed. This technology is used as an alternate of the previous bipolar, ECL and CMOS in the market. In some applications (in which there is finite budget for power) the BiCMOS speed performance is better than the that of bipolar. This technology is well suited for the intensive input/output applications. The applications of BiCMOS were initially in RISC microprocessors rather than traditional CISC microprocessors .

18. This technology excels its applications, mainly in two areas of microprocessors such as memory and input/output. It has a number of applications in analog and digital systems, resulting in the single chip spanning the analog-digital boundary. It overpass the gap permitting course of action and circuit margins to be crossed. It can be used for sample and hold applications as it provides high impedance inputs. This is also used in applications such as adders, mixers, ADC and DAC. To conquer the limitations of bipolar and CMOS  operational amplifiers  the BiCMOS processes are used in designing the operational amplifiers. In Operational amplifiers, high gain and high frequency characteristics are desired. All these desired characteristics can be gained by using these BiCMOS amplifiers.

19. Bibliography https://www.allaboutcircuits.com/textbook/digital/chpt-3/cmos-gate-circuitry/ https://www.elprocus.com/bicmos-technology-fabrication-and-applications/ https://www.elprocus.com/transistors-basics-types-baising-modes/ https://www.tutorialspoint.com/vlsi_design/vlsi_design_digital_system.htm

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