Second generation silicon capacitors boost performance
Empower Semiconductor has launched its second generation of silicon capacitor to take on multi-layer ceramic capacitor (MLCC) devices in wearable and IoT designs.
The e-cap silicon capacitors are built with a combination of trench design and process tweaks at TSMC, and produce a capacitance of 1.1µF/mm2, twice that of the previous generation, says Steve Shultis, EVP of sales and marketing at Empower.
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“The typical operating voltage of the first generation was 2V but this second generation is 4V with a double capacitor structure,” he said. “We have learned how to design the structure to double the voltage with less capacitance in a different way.”
The silicon capacitors are less that 50um deep and are built in an array of ten devices with individual pin outs to replace multiple MLCC devices. The matched capacitance values from 75pF to 5µF (@2V) can be integrated into a single die to create custom integrated capacitor arrays.
“2.2mm x 2mm is the biggest device we can make so the biggest capacitor is 4.8uF which is equivalent to 15uF in a ceramic capacitor,” said Sultis. “That 2 x 2mm array seems to be the sweet spot – we are also looking at arrays that are four capacitors on a smaller array,” he said.
“If I’m doing one to one replacement, MLCCs can be very cheap and silicon capacitors are not going to get that inexpensive,” he said. “The more capacitors I can fit in means I don’t have the cost factor. The cross over is typically 4 capacitors.”
There are different packaging options so that they can be used for decoupling capacitors in PCB modules but also for silicon substrates. This is especially helpful with higher frequency signals where MLCC designs require more device.
“For HF decoupling MLCCs require additional devices for higher frequencies,” said Shultis. “There are tradeoffs with the packaging – the fine pitch bumps are really good for substrate mounting with good ESR with little copper, while the pads have more copper so the ESR isn’t as good but easier to work with on PCBs.”
The technology has found traction with consumer design with PCB mounting says Sultis, particularly wearables and designs for the Internet of Things (IoT).
“It’s a custom engagement most times but you find a 100nF e-cap replaces a 0.1uF capacitor, so we can use one or two standard values of e-cap to replace all the decoupling capacitors in a design.”
This can be at the board level or in a package.
“Our foundry partner is TSMC and they announced their 3D packaging with silicon capacitors in the packaging, but all the other packaging guys need this. They don’t have the silicon trench process technology,” he said.
He also points out the silicon capacitor are not susceptible to low frequency noise in the same way as MLCCs and there is no nickel plating which can produce magnetic susceptibility.
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