Prashant Verma | Sub-Editor | ELETimes
Modern electronic devices are becoming smart and more efficient with the passage of time. They give high-performance computing power, 5G speed network support, auto pilot mode in EVs like Tesla, Artificial Intelligence (AI), and cloud computing. These features have made human life more comfortable than before because now modern processors can integrate tens of billions of transistors on a single silicon die by using advanced manufacturing nodes. While these innovations in semiconductors significantly improve computational performance, they also introduce a critical engineering challenge such as managing heat while maintaining a stable power supply throughout the chip.
A single operation in electronic devices can allow billions of transistors to operate simultaneously at frequencies exceeding several gigahertz and thus generate a substantial amount of heat. If the generated heat is not effectively dissipated, the chip’s temperature rises which can cause performance degradation or lagging of a system. Thus, thermal management plays a significant role in maintaining the temperature of semiconductor devices to ensure that the chip’s temperature is maintained throughout the operation.
Understanding Heat Generation in Semiconductor Devices
Heat in semiconductor devices is produced by the flow of electrical current during transistor operation. As electrons move through the semiconductor material, some kinetic energy is converted into heat because of the device’s internal resistance.
Modern digital electronics use CMOS transistors because of their high integration density and low power dissipation. It is used to manufacture nearly all integrated circuits (ICs). Every CMOS transistor consumes power through two primary mechanisms which contribute to heat generation.
- Dynamic Power
- Leakage Power
Dynamic Power: It is the energy consumed when a circuit actively switches between logic states (0 and 1). The primary role of dynamic power is to provide energy for switching the transistor between logic states. The higher the operating frequency and switching activity, the greater will be the consumption of dynamic power which will generate more heat.
Thermal management controls this heat through the following methods:
- System-Level Active Cooling: It provides cooling through fans or circulating dielectric liquid.
- Circuit and Architecture-Level Management: It lowers the supply voltage and clock frequency when there is less workload on the system.
- Semiconductor and Packaging-Level Dissipation: It includes dummy metals placed below hot CMOS junctions to draw heat away from the microscopic transistor level.
Leakage Power: It is defined as the electrical energy wasted as heat due to continuous current flowing through the semiconductor device even when the device is in idle state. Several physical mechanisms generate leakage in modern transistors such as subthreshold leakage, reverse-bias PN junction, and gate oxide tunneling. It is a major challenging problem in thermal management.
Following are the methods used to manage leakage heat:
- Power Gating: It is a circuit design technique that reduces power consumption by completely shutting off the power supply to idle regions of the chip.
- Dynamic Voltage and Frequency Scaling: Lowering the supply voltage and clock frequency during tasks that require low computation power to reduce overall power and subsequently lower operating temperature.
- Thermal Floor planning: It is a chip design technique to minimize leakage heat by strategically arranging different heat generating circuits across the chip. Thermal Management plays an important role in maintaining the optimal temperature of electronic devices.
What is Power Integrity?
While thermal management focuses on removing heat, power integrity focuses on delivering required stable power to every transistor on the chip so that the device operates efficiently under all operating conditions.
Why Power Integrity is required in Semiconductor Devices?
The major requirement of power integrity is to prevent voltage fluctuations and noise that can cause logic errors, timing failures, and performance degradation. Following are the list of primary reasons why power integrity is essential in modern semiconductor devices:
- Preventing Voltage Drop: Voltage practically drops when millions of transistors switch simultaneously. Power integrity minimizes voltage drop by minimizing the impedance of the Power Distribution Network (PDN).
- Controlling Clock Jitter: Clock jitter is the unwanted, short-term variation in the clock signal caused by noise sources such as power supply variations and electromagnetic interference.
- Reducing Electromagnetic Interference (EMI): A well-designed Power Distribution Network (PDN) delivers suitable power across the transistors of the chip that reduces electromagnetic interference which eventually reduces power consumption and improves thermal performance.
Major Power Integrity Challenges
Modern semiconductor devices deliver enhanced computational power. However, they also face critical power integrity challenges such as ensuring suitable power delivery across a chip, despite shrinking transistors size and massive current surge. Following are the key challenges in Power Integrity:
- IR Drop: Current flowing through the resistance (metal interconnects) causes voltage loss. This voltage reduction is known as IR Drop. In semiconductors, a higher current flowing through a resistive interconnect results in a large voltage drop. If the voltage reaching a functional block falls below its required operating level, functional errors may occur. Engineers must therefore optimize the power grid to minimize IR drop across the chip.
- Simultaneous Switching Noise (SSN): It is defined as the voltage fluctuations created within the power delivery network when multiple transistors switch simultaneously creating a sudden surge in current demand. If SSN is not controlled, it can cause timing errors, signal integrity issues, and unreliable operation. Engineers minimize Simultaneous Switching Noise (SSN) by optimizing the Power Delivery Network (PDN) and controlling on-chip switching dynamics.
- Power Supply Noise: It is defined as an unwanted variation in current and voltage on a DC power line. It includes high frequency spikes and voltage drops caused by switching regulators and high-speed switching of transistors inside the chip.
Power supplies are never perfectly stable. Without sufficient decoupling capacitance and well-designed power distribution network, Power Supply Noise occurs as voltage ripple across the chip. This problem is one of the major challenges in modern semiconductor devices because of simultaneous switching of billions of transistors, lower operating voltages, increasing clock frequencies, and high-power density.
Engineers reduce power supply noise by building on-chip decoupling capacitance, using thicker metal power grids to lower resistance, and integrating voltage regulators directly onto the chip.
Conclusion
Thermal management and Power integrity are closely linked to each other. As power delivery losses generate heat and increasing temperature slows down electrical efficiency and increases resistance. To prevent any hindrance in the performance of a system, these two disciplines must be perfectly balanced during the design process.
Modern semiconductor companies treat both thermal management and power integrity as a single discipline while evaluating throughout the design process using advanced Electronic Design Automation (EDA) tools. This co-optimization approach enables engineers to achieve higher performance, lower power consumption, and improved long-term reliability in advanced semiconductor devices.
