| ArkadiyB
| Joined: 17 Aug 2013 | Posts: 5 | |
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Posted: Sat Aug 17, 2013 12:23 pm Post subject: MEMS/cmos process to replace quartz oscillators? |
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MEMS/cmos process to replace quartz oscillators?
Almost every electronic product needs a clock to provide its 'heartbeat' and, traditionally, this heartbeat has been supplied by a quartz oscillator.
While there is nothing wrong with the basic principle of quartz oscillation, there are many elements of the production process which complicate things.
Initially, the quartz needs to be cut, lapped and polished before further operations create a crystal with the required performance. Because of this complexity, yield is a problem. And then, once the crystal is created, it has to be housed in a hermetically sealed ceramic package, along with a silicon amplifier. Only then can the device be tested to see if it meets requirements.
So it's no surprise to find that companies have been looking for other ways to address the timing requirements of electronic systems. One of those is Silicon Laboratories.
Mike Petrowski, general manager of the company's timing products division, believes quartz has had its day. "It only works on one frequency," he said, "it has long lead times and one of the biggest headaches is the supply chain." He also noted that quartz is a mature technology – almost 100 years old – which is susceptible to shock and vibration, as well as being a relatively high cost solution.
In fact, the company has been working on alternatives to quartz since 2004, when it introduced crystal oscillators (XOs) which brought mixed signal technology to bear on the issue. The result was devices which allowed almost any frequency to be generated from one crystal based reference frequency.
While the approach – called DSPLL – removed the need for unique crystals to generate specific frequencies and simplified the supply chain, the process still created multi-die products. Meanwhile, the industry was beginning to look at MEMS technology as a potential replacement for quartz, with companies such as Discera, SiTime and Epson undertaking some of the early work. Also making inroads into the technology was IDT with its pMEMS based products.
An acquisition made in 2010 brought Silicon Labs into the race. It bought Silicon Clocks, an early stage company creating MEMS based timing technology. Its CMEMS – standing for cmos plus MEMS – technology allowed MEMS resonators and other sensor structures to be created directly on standard cmos wafers. The approach did away with the need for special semiconductor processing for the MEMS elements and addressed performance, integration and size issues. It also addressed parasitics and packaging issues.
"We made the acquisition with the goal of being a one stop timing shop," Petrowski claimed.
Now, Silicon Labs has launched CMEMS based devices. One of the advantages is a shorter manufacturing process. "It's just like making a chip," Petrowski continued. "We can make these parts in less than two weeks, compared with 12 weeks for quartz."
The Si50x range is said by Silicon Labs to feature the most highly integrated MEMS based oscillators currently available. The range has been designed to replace general purpose crystal oscillators in cost sensitive, low power and high volume industrial, embedded and consumer electronics applications.
"The Si50x family introduces an important technological step forward," said Petrowski, "combining all the manufacturing advantages of a single die MEMS based solution, while retaining some of the best characteristics of general purpose crystal oscillators and improving on reliability and lead times."
The manufacturing process starts with standard passivated cmos wafers. Polycrystalline SiGe and pure germanium are then surface micromachined to create integrated MEMS devices on top of the cmos circuitry and interconnects. With the MEMS structure in place on the cmos wafer, a full oscillator system is created. The devices can then be encapsulated in a vacuum. The result is timing devices which are guaranteed to have a frequency stability of ±20ppm over 10 years, along with high shock and vibration resistance. _________________ tax relief new york city |
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