The silicon speakers redefining sound

The world of audio is always a rapidly changing market and the new trend of wireless, in-ear headphones (known as ‘hearables’) are no exception. Hearables are wireless in-ear devices that can be used for a variety of applications ranging from medical heartbeat monitoring to wireless transmission and fitness tracking. Reece Webb reports.

Arioso Systems, a spin-off company of the Fraunhofer Institute for Photonic Microsystems IPMS, is bucking the trend by developing a micro in-ear loudspeaker made from 100% silicon MEMS (micro-electromechanical systems) based on Nanoscopic Electrostatic Drive (NED) technology developed by the IPMS to offer a lighter, longer-lasting hearable experience unlike any other on the market.

Jan Blochwitz-Nimoth, one of the founders and managing director in charge of finance, Arioso Systems, has a strong background in starting up small and medium size companies in the technology and innovation fields. 

Blochwitz-Nimoth said: “The original idea originated in 2010 as a by-product of PHD work at IPMS by Arioso’s co-founder Holger Conrad.” 

“I came to the team when they were working on papers for the Nature journal. Hermann Schenk, a senior manager from the semiconductor industry and Arioso’s managing director in charge of technology, already investigated the commercial potential and thought that forming an independent venture capital financed company would be the best way to commercialise because it’s still very novel and disruptive technology, but it has huge potential. He invited me to join Arioso.“

The technology differs to conventional micro-loudspeakers relying on moving coils and plastic diaphragms. Using silicon allows the technology to be deployed in a way that is smaller, lighter and easier to manufacture on a large scale. 

Blochwitz-Nimoth said: “First MEMS based micro-speakers, recently entering the market, using lead-zirconate-titanate (PZT) materials to move a diaphragm by means of piezo electricity: if you apply voltage, PZT changes its shape thereby driving the speaker. In our solution a voltage is applied between two capacitor plates, generating a mechanical force between the two plates. 

Close up chip
"In a typical silicon MEMS factory, lead containing materials such as PZT, are not admitted. Therefore, we wanted to find something which is capable of moving things without using PZT while ensuring a very low power consumption. If you arrange tiny capacitors in a clever way, you can lever the generated force to bend cantilevers with large deflection. This is called NED technology, Nanoscopic Electrostatic Drive.”

The technology draws its name from the nanoscale of the capacitors and the use of electrostatic force that provides drive. 

“Electrostatic loudspeakers are considered the ‘holy grail’ of loudspeaker design and while electrostatic speakers can be expensive, from a high-fidelity standpoint they are exceptional.” – Jan Blochwitz-Nimoth, Arioso Systems

The silicon-based transducer does not use a conventional membrane, instead a series of bending cantilevers are arranged inside the body of a silicon chip.

These electrostatic actuated cantilevers have a width of 20 µm and a length of up to 2 mm, becoming energised by vibrations from the audio signal voltage to become intelligible as sound. The components can be integrated directly into the silicon chip, with the micro loudspeaker being designed for in-ear headphone or ‘hearable’ applications.

Blochwitz-Nimoth explained: “The funny thing with loudspeakers is that everything is based on 100-year-old technology. In every loudspeaker there is a magnet which makes the loudspeaker heavy and also can interfere with other electronic devices.

"They are quite big and difficult to make on a large scale of millions of units because the housing needs to be assembled manually. Most of the parts in today’s high-end headsets are already using silicon chips that are densely packed inside a tiny housing. The hitherto unmet need is to replace the bulky conventional moving coil speaker by a small silicon chip as well.

“Today’s speakers are roughly 10 millimetres in diameter and four to five millimetres thick. We are targeting a size of 10-13 mm² with a thickness of 1-2 mm. The volume that is covered by the speaker today inside the tiny in-ear headphone devices is painfully high. We are designing speakers below fifty cubic millimetres - it's a very small chip. Our technology saves a lot of space and a lot of weight, allowing this extra available space and weight to be used for smart functions, such as speech recognition, internet connectivity and batteries. That’s exactly what Arioso’s customers need for their advanced hearable applications.” 

Blochwitz-Nimoth notes that the technology is specifically geared towards applications which are smaller in size: “If a speaker comes in the format of a silicon chip instead of a delicate mechanical assembly, it is possible to automate the production of the devices enabling their production on a mass scale in existing MEMS factories.” 

“Silicon is always the best solution for high volume in-ear applications and devices which are small in size. If you have the technology to create a micro-speaker and its drive electronics on a small silicon chip, it is the most attractive solution due to the unprecedented cost efficiency of the silicon industry. This miniaturisation of micro-speakers as a fully integrated silicon solution is exactly Arioso’s outstanding competitive advantage.” 

Doing more with less weight in smaller environments is key to the development of commercially viable ‘hearable’ technology as Blochwitz-Nimoth added: “People want convenient to wear in-ear headphones which themselves are directly connected to the internet all day long. Hence more electronics is necessary, and every component must be small and lightweight and very power efficient.”

“We still have to work on fully implementing our technology over the next 12 months, followed by long-term testing before we can hit the market on a large scale with a product within the next three-four years. We aim to work with customers and motivate them to help expediting the micro-speaker development at Arioso.”

Blochwitz-Nimoth closes: "Inherently, the audio quality of Arioso’s micro-speakers should be excellent; electrostatic loudspeakers are considered the ‘holy grail’ of loudspeaker design and while electrostatic speakers can be expensive, from a high-fidelity standpoint they are exceptional. With our chip-based ideas we make this electrostatic approach feasible for in-ear headphones and hearables both technologically and price-wise.”

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