Harmonizing Circuit Design and EMC DesignPart 2 Summary of Semiconductors (2) Semiconductor Integrated Circuits (LSIs, ICs)

Hello! Inagaki of ROHM here.

In this second column, I’ll be talking about semiconductor integrated circuits. In general, large-scale integrated circuits and general integrated circuits are referred to by their acronyms, LSIs and ICs. Thus the name changes depending on the scale of the circuit, but it’s not like there is a clear line of demarcation. The old-timers (?) generally just called them all “ICs”. As you know, with a single transistor, operation is simple, but by forming many transistors on the same silicon substrate, complicated functions and highly precise circuit operations can be achieved. Combining transistors to create excellent circuits is the main mission of the designers of semiconductor integrated circuits (LSIs and ICs).

Currently, ROHM is mass-producing a total of 5,115 products, including, as principal product groups, 3480 power management/power supply ICs, 652 memory devices, 396 linear amplifiers, 259 motor drivers and actuator drivers, and 133 audio ICs and video ICs. The number of types of LSIs and ICs is only second to the variety of transistors and diodes. By transitioning from previous custom items to general-use products, ROHM has greatly expanded its semiconductor integrated circuit (LSI, IC) product lines.

When I joined ROHM some 30 or so years ago, the minimum trace widths or gate lengths of bipolar devices and CMOS devices was around 10 μm (10×10^-6 m), but according to recent news, work has begun overseas to develop a CMOS device with a trace width of 2 nm (2×10^-9 m) (with completion expected in 2022). Compared with the earlier devices, then, miniaturization has advanced to where the minimum processing dimension is just 1/5,000 as great. This is quite an amazing figure, and will mean that the manufacture of minimum gate lengths equal to several atomic diameters will be achieved in mass production processes. Truly spectacular! In fact, this miniaturization trend is associated with a famous law, called “Moore’s law”, after its originator at U.S. Intel Corp. The law states that miniaturization will be such that integration levels will double every 1.5 to two years. The central processing units (CPUs) manufactured by Intel have followed this law. And even the ” IEEE International Roadmap for Devices and Systems”, or IRDS, makes detailed predictions of future manufacturing processes along these lines. Persons who are interested can do a web search; it is quite interesting (https://irds.ieee.org/)! When miniaturization of the dimensions of transistors in semiconductor integrated circuits (LSI, ICs) proceeds in this way, ever greater numbers of transistors can be integrated for a given chip size, so that more sophisticated functions become possible. Moreover, the rated voltage of the semiconductor devices is lower, but the operating voltage is also lower, and the battery run time can be extended. Also, the parasitic capacitance of smaller semiconductor devices is lower, so that device operation is faster and improved performance is possible.

Well then, let’s have a look at the relationship between electromagnetic compatibility (EMC) and miniaturization! Where electromagnetic interference (EMI), in which a device itself emits electromagnetic noise, is concerned, as miniaturization advances, the reduced operating voltage is accompanied by a decline in low-frequency electromagnetic noise, and due to the reduced parasitic capacitance there is a tendency for the operating frequency to rise and for high-frequency noise to increase. As for electromagnetic susceptibility (EMS), in which external electromagnetic noise causes a malfunction, with increasing miniaturization the operating voltage is lowered and the noise tolerance (noise margin) is decreased, so that, as a result of the greater sensitivity, malfunctions occur more readily (a mental image here is important!). Hence it is not the case that the latest manufacturing processes are beneficial in all ways, and where electromagnetic compatibility (EMC) is concerned, there are many aspects in which semiconductor integrated circuits (LSIs, ICs) mass-produced using somewhat older manufacturing processes are better.

For example, in the case of differential operational amplifiers (op-amps), it is better to select a product that secures the minimum required operation frequency band. If a product is used with an operation band that is broader than needed, extending to higher frequencies (manufactured using more advanced miniaturization processes), then it is necessary to perform additional verification of electromagnetic compatibility (EMC) at high frequencies. And, general-use logic and other products should not be chosen having an operation voltage that is lower than needed. Moreover, for products that will execute complicated functions, there are various measures (techniques) and design methods to improve electromagnetic compatibility (EMC). These methods are also described in application manuals for the respective products, and I would like to introduce a number of them in some detail in this column. Please watch this space!

Thank you for your attention.