What is CMOS? Working Principle & Its Applications
Table of Contents
- jaro Education
- 11, July 2024
- 5:00 pm
CMOS stands for the foundation of modern integrated circuits powering smartphones and laptops, digital cameras, and, more recently, smart home devices. Even though other technologies are coming onto the scene, CMOS technology still holds more than 90% of the semiconductor market, with its low power consumption as well as better efficiency and scalability.
According to MarketsandMarkets, the CMOS image sensor market is expected to generate revenues of USD 29.2 billion by 2027, at a CAGR of 7.3%. Such numbers underline the technology’s relevance not only in computing but also in AI vision systems, automotive safety, and industrial automation.
Now we are entering the era of 5G, AI, and IoT. This stage sets the highest demand for semiconductor devices to be compact, power-efficient, and high-speed. To fulfill this demand, CMOS technology is being upgraded with innovations like FinFETs, 3D ICs, and nano-CMOS, which are helping to push the envelope of Moore’s Law.
What is CMOS?
CMOS is the short-term solution for Complementary Metal Oxide Semiconductors. In the computer chip design business, CMOS technology is one of the most widely used technologies that help create integrated circuits in various applications. It is a popular MOSFET technology used in today’s computer memory, CPUs, and mobile phones because it has numerous advantages. Semiconductor devices like the P and N channels are used in and define what CMOS is, which is also known as PMOS and NMOS. With CMOS technology, relevant professionals can design microcontroller chips, microprocessors, RAM, ROM, Application Specific Integrated Circuits (ASICs), and EEPROM. Knowing about CMOS working principles and the application of CMOS is important before using it.
Types of Transistors in CMOS
Types of transistors in CMOS are p-transistors and n-transistors. Although these materials can conduct electric current, depending on the conditions, such conduction will be found neither here nor there. The characteristics of a semiconductor prohibit an answer to the question of whether it behaves, in terms of conductivity, as a conductor or as an insulator. Semiconductors consist of silicon and impurities, which together make up a critical condition for conductivity.
So, obtaining pure silicon does not allow current to pass. It manipulates current conditions between its source and drain terminals based on a certain amount of applied voltage and acts as an amplifier or switch.
Doping is the process by which impurities are introduced into a substance like silicon. Semiconductor doping can be varied to a certain extent to control the conductivity. However, there are other determining factors affecting conductivity that have nothing to do with the impurity types used.
In a different aspect, the impurities depend on the type of semiconductor material used in MOSFETs. MOSFET semiconductors can be either p-type or n-type. P-type semiconductors use substances like boron, gallium, and indium. N-type semiconductors use phosphorus, arsenic, and bismuth.
The positively charged p-type semiconductor carries current as electron-hole pairs. A hole will have a positive charge equivalent to an electron charge. Electrons move in the opposite direction to holes. The n-type semiconductor is negatively charged. It represents the renewable energies in this case; thus, the semiconductor carries the current in the form of negatively charged electrons.
How was CMOS Developed?
George Sziklai established the notion of complementary symmetry in 1953. However, Frank Wanlass of Fairchild Semiconductor invented the Complementary Metal Oxide Semiconductor technique. He, along with Chih-Tang Sah, demonstrated at the 1963 International Solid-State Circuits Conference. Wanlass later submitted a US patent on Complementary Metal Oxide Semiconductor circuitry, which was issued in 1967.
What is its working principle?
The CMOS circuit uses both P-type and N-type transistors to create logic functions, which are essential components in designing integrated circuits. The signal that turns ON one type of transistor can also turn OFF another type of transistor. This feature enables the creation of logic devices with simple and basic switches and no pull-up resistors.
The CMOS logic family includes n-type MOSFETs (transistors) arranged in a pull-down network that connects the output to the low-voltage power supply rail (Vss or the ground). Furthermore, Complementary Metal Oxide Semiconductor logic gates use a pull-up network of p-type MOSFETs between the output and the higher voltage rail (commonly known as Vdd) instead of load resistors like NMOS logic gates. So, if both p-type and n-type transistors have their gates linked to the same input, the p-type MOSFET will be ON while the n-type MOSFET is off, and vice versa.
Complementary Metal Oxide Semiconductor has relatively low power loss, high noise margins in both modes, and fast speed, and it can function over a broad range of source and input voltages (provided the source voltage is fixed). Furthermore, to better grasp the Complementary Metal Oxide Semiconductor (CMOS) working principle, you must briefly explore Complementary Metal Oxide Semiconductor logic gates.
Trends and Innovations
The following trends and innovations are impacting the future of CMOS technology:
- CMOS is being integrated with new technologies to address both old and current demands
Emerging Trends:
- FinFET & GAA (Gate-All-Around) Transistors:
Used by TSMC, Samsung, and Intel at 5nm and 3nm chip nodes - 3D CMOS Architectures:
Stacking multiple layers to increase density and speed.
- AI-Optimized CMOS:
Coupled with neural engines for edge computing applications of CMOS. - Photonic CMOS:
Integrating light with electronics for accelerated data transfer.
- CMOS in Quantum and Neuromorphic Computing:
Used as an interfacing medium for quantum processors or brain-inspired chips.
What Is The Advantage Of CMOS Technology Over Bipolar Technology?
The main advantage of CMOS over bipolar technology is its significantly lower power dissipation. In contrast to bipolar circuits, a complementary MOS circuit has little static power dissipation. Power is only dissipated if the circuit switches. This enables the integration of more Complementary Metal Oxide Semiconductor gates on an IC than in NMOS or bipolar technology, resulting in much-improved performance.
What Is CMOS Logic Family?
Let’s assume a Complementary Metal Oxide Semiconductor inverter circuit consists of p-type and n-type MOSFETs. Input A will serve as the gate voltage for both transistors.Â
The NMOS transistor will receive input from Vss (ground), while the PMOS transistor will receive input from Vdd. For output, the Y terminal will be used. When a high voltage (~ Vdd) is applied to the inverter’s input terminal (A), the PMOS opens and the NMOS switches off, causing the output to be pushed down to Vss.
When a low voltage (<Vdd, ~0V) is provided to the inverter, the NMOS turns off, and the PMOS turns on. So, the output becomes Vdd, or the circuit is brought up to Vdd.
| Input | Logic Input | Output | Logic Output |
|---|---|---|---|
| 0v | 0 | Vdd | 1 |
| Vdd | 1 | 0v | 0 |
What is the CMOS NAND gate?
Suppose there’s a 2-input CMOS NAND gate consisting of two series NMOS transistors between Y and ground and two parallel PMOS transistors between Y and VDD.Â
If either input A or B is logic 0, at least one of the NMOS transistors will be turned off, interrupting the flow from Y to ground. However, at least one of the pMOS transistors will be active, forming a channel from Y to VDD.
Thus, the Y output will be high. If both the inputs are high, both NMOS transistors will be ON and both the PMOS transistors will be OFF. Consequently, the output will be low. The truth table of the NAND gate is shown in the following table.
| A | B | Pull-down Network | Pull-Up Network | Output Y |
|---|---|---|---|---|
| 0 | 0 | OFF | ON | 1 |
| 0 | 1 | OFF | ON | 1 |
| 1 | 0 | OFF | ON | 1 |
| 1 | 1 | ON | OFF | 0 |
What is the CMOS NOR gate?
To explain this, let’s consider a 2-input NOR gate. When either input is high, the NMOS transistors in parallel pull the output low. The PMOS transistors are connected in series to pull the output high when both inputs are low. Hence, the output is never left floating.Â
The truth table of the NOR gate is given in the table below:
| A | B | Y |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 0 | 1 |
What is the Fabrication of CMOS?
Complementary metal oxide semiconductor transistors can be fabricated on silicon wafers. The diameter of the wafer varies from 20mm to 300mm. In some cases, the lithography process is identical to the printing press. At each phase, different materials can be deposited, etched, or patterned. This procedure is fairly straightforward to grasp by looking at the wafer’s top and cross-section using a simplified assembly method. Complementary metal oxide semiconductor manufacturing may be achieved by utilizing three technologies: N-well or P-well, twin well, and SOI (silicon on insulator).
What are the Characteristics of CMOS?
The most important characteristics of Complementary Metal Oxide Semiconductor are its low static power utilization and high noise immunity. When a single transistor from a pair of MOSFET transistors is turned off, the series combination consumes substantial power while switching between the two states, ON and OFF. Therefore, these devices produce no waste heat compared to other logic circuits, such as TTL or NMOS logic, which often require some standing current even while their state remains constant.
These features will enable the integration of logic functions in high density on an integrated circuit. As a result, Complementary Metal Oxide Semiconductor has emerged as the most widely utilized technology for VLSI chips.
The term MOS refers to the physical structure of a MOSFET, which consists of an electrode with a metal gate atop a semiconductor oxide insulator. A substance like aluminum is only used once, but it is now polysilicon. Using high-κ dielectric materials in the complementary metal oxide semiconductor process can enable the creation of additional metal gates.
What are the Applications of CMOS?
Complementary Metal Oxide Semiconductor technology is widely used and has largely superseded Bipolar processes in almost all CMOS applications in digital electronics. The following integrated circuits were designed using Complementary Metal Oxide Semiconductor technology:
- Image Sensors
Complementary Metal Oxide Semiconductor image sensors are utilized in CMOS in digital electronics cameras to turn pictures into CMOS in digital data. - Microprocessors and Microcontrollers
Complementary Metal Oxide Semiconductor technology is used in the creation of microprocessors and microcontrollers, which are critical components of many electronic devices.
- Analogue Circuits
Analogue circuits using Complementary Metal Oxide Semiconductor technology include data converters, RF (radio frequency) circuits, and highly integrated transceivers for a variety of communication applications of CMOS.
What are the Benefits of Using CMOS?
Here are the advantages and disadvantages of CMOS:Â
The main benefit of CMOS over other technologies (TTL) is its excellent noise margin and lower power consumption. This is owing to the lack of a straight conducting channel from VDD (drain power voltage) to GND (ground), which causes fall times that are dependent on input circumstances, making CMOS in digital electronics signal transmission straightforward and low-cost using Complementary Metal Oxide Semiconductor devices.
Complementary Metal Oxide Semiconductor explains the amount of memory on a computer’s motherboard that is used to save BIOS settings. These settings typically comprise the date and time, as well as hardware settings.Â
The common benefits of CMOS technology are:
- Compatible with TTL
- Complementary Metal Oxide Semiconductor logic uses less power whenever it is in a set state
- Low power dissipation
- The logic gates are very basic
- Fan out is high
- Compact
- Noise immunity is good
- Mechanically very strong
- Input impedance is high
- Large logic swing
- Stability of temperature
What are the Disadvantages of CMOS?
The disadvantages of CMOS are as follows:
- As compared to bipolar technologies, the packing density of Complementary Metal Oxide Semiconductor is low.Â
- When the processing steps increase, the cost of Complementary Metal Oxide Semiconductor also becomes high. However, there may be a solution to this problem.Â
- Another disadvantage of the Complementary Metal Oxide Semiconductor technology is that it requires two transistors to construct an inverter rather than one transistor, which means that the Complementary Metal Oxide Semiconductor takes up more space on the chip than the NMOS.Â
- Complementary Metal Oxide Semiconductor chips should be protected against static charges by shorting the leads; otherwise, static charges obtained within the leads will destroy the chip.
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Conclusion
For efficient electrical power, using CMOS technology is a suitable choice. They do not need an electrical supply while transitioning from one condition to another. Furthermore, the complementary semiconductors operate together to block the o/p voltage. This results in a low-power architecture that generates less heat. For this reason, CMOS has replaced previous designs, such as CCDs, in photosensors. CMOS is also utilized to design ICs, computer memory, non-volatile RAM, and so on.
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