Published: January 30, 2025
Table of Contents
Analog Circuits and Miniaturization
Scaling Analog Circuits: The Case of Power Management ICs
Power Management IC and Fine Process
Integration of Analog Functions
This is the final volume of the miniaturization series. In this volume, I will discuss the miniaturization of analog circuits.
Click below to read past volumes,
Volume 1: Semiconductor Miniaturization: What is Moore's Law?
Volume 2: Semiconductor Miniaturization and Manufacturing Process
Volume 3: Semiconductor Miniaturization and International Technology Roadmap
Volume 4: Semiconductor Miniaturization and Semiconductor Business
Volume 5: Semiconductor Miniaturization and Semiconductor Business (Part 2)
Volume 6: Semiconductor Miniaturization and Semiconductor Devices
Volume 7: Semiconductor Miniaturization: What is MOSFET Scaling?
Volume 8: Semiconductor Miniaturization: Limitations of MOSFET Scaling
Volume 9: Semiconductor Miniaturization and Analog Circuits
As I mentioned in volume 7, miniaturization (scaling) offers significant advantages for digital circuits. In fact, it may not be an overstatement to say that miniaturization (scaling) is primarily meant for digital circuits.
But what about analog circuits? Denard’s original paper on MOSFET scaling was, after all, written with digital circuits as its focus. This is based on what I have seen and heard, as I am not a circuit designer, (and although it may be difficult to generalize given the wide variety of analog circuits), it seems that analog circuits do not always benefit from miniaturization (scaling) and may even face disadvantages in many cases. For example, miniaturization based on MOSFET scaling leads to a reduction in supply voltage, which does not seem advantageous for analog circuits.
In digital circuits it is sufficient to distinguish high voltage as "1" and low voltage as "0", so in this sense the absolute value of the voltage is not particularly significant. In contrast, for analog signals, the magnitude and shape of the signal itself carry meaning. Therefore, the role of voltage in analog circuits can be considered fundamentally different from its role in digital circuits.
Let’s dive into a specific example. Analog circuits include various types, such as operational amplifiers, A/D and D/A converters, and high-frequency circuits, and the situation will be different for each. Here, I will focus on power management ICs, one of our flagship product lines.
For more information on power management ICs, please visit our website’s “Power Management IC Basics” page.
Before considering whether MOSFET scaling can be applied to power management ICs, for example, let's take a look at a DC/DC converter (DC/DC switching regulator) system that converts DC voltage, as shown in the figure below. The DC/DC converter system requires not only a power management IC ("DC/DC converter" in the figure), but also external components such as capacitors ("CIN/COUT") and an inductor ("L") to function. In other words, a DC/DC converter system cannot be fully integrated into a silicon chip. Therefore, as a complete system, it lies (I am not sure if this is the right word) outside the scope of Moore's Law and MOSFET scaling.
Note: Moore's article in 1965, the so-called Moore's Law, ("Cramming more components onto integrated circuits," Electronics, Volume 38, Number 8, April 19, 1965), which I discussed in the first volume, contains the following statement. “Integration will not change linear systems as radically as digital systems. Still, a considerable degree of integration will be achieved with linear circuits. The lack of large-value capacitors and inductors is the greatest fundamental limitations to integrated electronics in the linear area.” (In this context, the term “linear” can be interpreted as referring to analog systems.)
DC/DC Converter (DC/DC Switching Regulator) System
Now let’s consider whether MOSFET scaling can be applied to power management ICs. Unfortunately, the conclusion is that it cannot.
The primary function of power management ICs is to generate and supply the optimal voltage for operating electronic components, such as ICs, from a power source such as AC power supplies or batteries. For example, the R1524, one of our best-selling LDO linear regulators, operates with an input voltage range of 3.5V to 36V from an upstream power source and delivers a preset output voltage between 1.8V and 12V to the subsequent stage. Because the operating voltages are predetermined by the product's specifications, voltage scaling is inherently not applicable. The absolute value of the voltage is meaningful in this context, so scaling would result in a different product.
Additionally, since this product handles input voltages as high as 36V, scaled fine process transistors would fail under such conditions. In fact, the key role of this product is to convert high input voltages into levels that fine process transistors can handle safely without being damaged.
Block Diagram of R1524
Even though simple scaling may not be feasible, is it meaningless to use fine processes for power management ICs?
In terms of miniaturization for higher circuit integration, the impact on power management ICs is minimal. This is because power management ICs are inherently single-function devices. All the circuit elements required to achieve the functions of power management ICs and that can be integrated on a silicon chip are already integrated. Therefore, while there may be some additional functions, power management ICs can barely benefit from further miniaturization in terms of functional integration.
Also, as mentioned in the previous section, since the voltage is fixed and cannot be lowered, small transistors in fine process cannot be used due to the risk of breakdown. Thus, the benefits of using fine processes for higher integration in analog circuits are not as significant as in digital circuits.
However, using advanced microfabrication techniques in fine processes enhances the precision of pattern formation and enables the use of finer patterns. While fine transistors cannot be employed, adopting finer processes is still beneficial where possible. Improved patterning precision is expected to enhance the accuracy of analog circuits, and even if transistor scaling is not possible, analog circuits can still be made smaller by leveraging finer patterns and greater precision.
That said, as of 2021, utilizing cutting-edge 7nm or 5nm fine process technologies requires investing in lithography systems costing over 10 billion yen. Even equipment from the previous generation costs several billion yen. Establishing such systems and developing processes solely for single-function analog products like power management ICs would be impractical.
While it is true that 5nm and 7nm fine process technologies are overly advanced for such applications, fine process technologies are sometimes leveraged to create dedicated processes for analog products such as power management ICs in fabs originally designed for digital logic products. This approach is a practical way to repurpose older fabs.
At our company, we have developed and utilized processes for single-function power management ICs based on the fine process (at the time) initially developed for other product lines. However, because power management ICs, especially those handling high voltages (high-voltage products), cannot be manufactured using processes designed for digital circuits, additional measures are required, such as introducing processes for creating devices specifically dedicated to power management ICs.
Note: Of course, companies specializing in analog products would likely have developed analog-specific processes in fabs dedicated to analog production from the outset.
Let me briefly discuss high-voltage transistors used in power management ICs designed to handle high voltages. The scaling I have described so far has been in the direction of reducing both the size of the device and its operating voltage. However, high-voltage transistors go in the opposite direction because they are designed to handle higher voltages. In other words, high-voltage transistors become larger.
So far, I have used single-function power management ICs as examples of analog products. In systems, multiple types of power management ICs are often required, so integrating these into a single chip provides benefits such as reducing the mounting area. Since digital logic circuits may also be included, miniaturization has some value. However, the integrated logic circuits are usually not very large, so using a moderately fine process is sufficient. Aggressively pursuing further miniaturization offers minimal benefit.
For more information on our products with integrated power management ICs, please visit our website of “PMICs” and “PMICs Strengths and Track Records.”
In terms of function integration, beyond the integration of multiple power management ICs, analog functions, including power management ICs, can also be integrated as part of the trend toward integrating all system functions into a single chip. However, as mentioned earlier, the voltage of power management ICs cannot be scaled, which means that transistors designed for fine processes for digital circuits cannot be used.
Therefore, when integrating a power management IC, it is necessary to develop transistors specifically for power management ICs in addition to the standard transistors used for digital circuits. This increases the complexity and length of the manufacturing process. Even if the power management IC is integrated into a chip using a fine process, the power management area does not benefit significantly from miniaturization. Consequently, whether to integrate it into the same chip should be carefully assessed on a case-by-case basis.
So far, I have discussed miniaturization and analog circuits, focusing on power management ICs as an example. As I mentioned at the beginning, this concludes my blog on miniaturization. In the next volume, I plan to address the second major trend in semiconductors: the shift toward larger diameter wafers.