Inductor Guide

Anecdote of inductor development [No.2] Birth of the first film-type inductor: the "LQP31A series"

The first film-type inductors, the "LQP31A series," were created about 20 years ago, in 1991. They were completely different from the conventional chip-type inductors wound with copper wire. An electrical conductor approximately  a few dozen μm in width was wound into a swirl shapre, similar to a mosquito repellent coil, and a tiny inductor of the nH order was formed using thin-film processing to create the world's first chip inductor for high-frequency applications.
It was ultra-thin and ultra-compact (3.2 mm × 1.6 mm × 0.5 mm) and was formed with high dimensional precision by photolithography,* so that it achieved a much lower deviation of only ±2% compared to the ±10% that was the inductance deviation for chip inductors at the time. It was commercialized for use in high-frequency circuit applications such as cell phones, car phones and other mobile communications devices as well as BS tuners and other devices.

At the time, cell phones and car phones were very expensive items only owned by wealthy individuals. They were huge by today's standards and certainly not an item just anyone could easily carry around with them. During that time period, when people saw documents saying that the cell phone market was going to grow, they were skeptical.
It was against this backdrop that I was put in charge of development in 1989, my first year at Murata Manufacturing. I was completely out of my field and everything was unknown. Not only that, but this was to be the first attempt for the Department to try such a process, so we had to start completely from scratch, without even any equipment to perform test production. We began by launching a clean room and gathering beakers and other equipment, and completed our test production line in 1990. To call it a "test production line," however, is somewhat misleading -- it was more of a lineup of manual processes, like dipping a rubber-gloved hand into a container of solvent and shaking a wafer in the liquid to perform etching. It was a test production line full of "home-made" aspects.
We began development with this test production line, and repeated test experiments again and again using concoctions of different chemicals. Despite our efforts, our patterning continued to be unsuccessful. Day after day, we continued battling the unknown and searching hard for a solution. We were ecstatic when we first succeeded at patterning, but over six months had already passed.
We continued development even after that through trial and error, and it was not until 1991 -- two years after the start of development -- that we finally achieved the performance and reliability required for a product. Mass production was launched at a scale of about 20,000 units a month. For the so-called "mass-production line," we still used a manual processing line similar to our test production line. Needless to say, it cost several times more than contemporary winding wire-type inductors, and marketing was extremely difficult. The introduction of the LQP31A series was, however, the first step leading up to compact high-frequency inductors such as the 1005 size, 0603 size and then the 0402 size. In today's smartphones, a single phone uses dozens of these inductors, and they are being produced at a rate of tens of thousands of times greater than when we started out. Even now, that original test production line from 20 years ago continues to be upgraded and used for development and trials and works hard even today creating new value.


Photolithography: A technique in which the surface of a material coated with a light-sensitive chemical is exposed to light in a pattern (the light-sensitive chemical is exposed to light, causing it to react) so that the exposed parts and non-exposed parts form a pattern, and the material is then submerged in developer to remove the excess chemical. It is mainly used in production of parts such as semiconductor devices, PCBs, printing plates, LCD panels and plasma display panels.


Person in charge: K.M., Components Business Unit, Murata Manufacturing Co., Ltd

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