by John Williamson
Contributing Editor, MEMS Investor Journal
MEMS based oscillators are increasingly being used as an alternative to quartz in a growing number of electronic systems. According to our estimates, the global market for MEMS oscillators was $21.4 million in 2010 and is expected to reach $312 million by 2014, with consumer products representing nearly half of the market. The gains are based on manufacturers’ successful efforts to overcome earlier limitations of MEMS based oscillators in specific market segments while directly targeting the drawbacks of quartz based devices.
Todd Borkowski, Director of Product Marketing at Sand 9, says that earlier MEMS challenges included high power consumption, large phase noise, strong jitter, frequency jumps and strong spurious output. “While this is OK for low-end timing solutions it doesn’t work for precision timing requirements of 3G, 4G or GPS applications,” Borkowski says.
Other earlier issues included stability problems because of silicon’s temperature properties and contamination deposits on MEMS oscillator beams.
Companies such as Discera, Sand 9, Silicon Labs, SiTime, and Vectron are addressing these issues by providing MEMS based alternatives to quartz oscillators in high-volume applications such as consumer electronics, telecommunications and automotive.
These developments are aimed at overcoming disadvantages of quartz-based devices that include manufacturing cost, longer procurement times, scalability and susceptibility to shock damage. SiTime recently noted that as clock frequency increases, quartz-based SAW and overtone devices suffer in features, performance, availability, and size. This forces compromises, SiTime says. Similar issues have been cited by Vectron.
Performance measures for MEMS devices
According to Dr. Hisham Haddara, CEO of Si-Ware Systems, a check list to evaluate the performance of MEMS based oscillators should include frequency range and resolution, stability and tolerance, jitter, power consumption, temperature range and driving capability. MEMS Investor Journal looked into the recent developments in MEMS based oscillator technologies and outlined the key performance metrics in this detailed interview with Dr. Haddara.
To the question of where MEMS oscillators demonstrate advantages over quartz or IC designs, Mike Petrowski, General Manager of Timing Products at Silicon Labs responds: “MEMS resonators in general are more reliable than quartz crystal resonators in that they will operate reliably at high sustained temperatures and have a higher tolerance for mechanical shock. Moreover,” he adds, “MEMS resonators are smaller in size than comparable crystal resonators and can therefore lead to the realization of oscillators in small packages where size is an important consideration.”
Sand 9’s Todd Borkowski lists the prime advantages of MEMS as vibration immunity, shock resistance, power supply noise immunity, small package dimensions, and availability. “These are common attributes offered by all MEMS oscillator suppliers versus quartz suppliers,” he says.
Addressing high shock and vibration applications, Vectron International in 2008 introduced “the industry’s first” high-shock oscillator. According to the company, it is capable of resisting shock up to 100,000 g. Depending on the model, Vectron’s MEMS oscillators exhibit frequency stability from 25 to 100 ppm (parts per million) over temperature ranges from -40 to 85˚C. With output frequencies to 150 MHz, the development targets military applications.
Frequency stability or tolerance over temperature is a measure of oscillator quality because drift may negatively affect the performance of the system. In these cases, lower ppm numbers are better but can represent an increase in cost. SiTime earlier this year stepped up to this with its SiT8003 and SiT8103 programmable MEMS oscillators that deliver 25 ppm stability at the same price as its 50 and 100 ppm devices for networking, storage, consumer and industrial applications. In the latter case, a temperature range of -40 to +85°C is supported.
At Sand 9, work focuses on temperature controlled MEMS oscillator (TCMO) technology. Todd Borkowsky says this is the industry’s first MEMS oscillator offering phase noise performance and short term stability comparable to temperature controlled crystal oscillators (TCXOs) along with high accuracy. “To illustrate,” he says, “typical TCXO phase noise requirements for cellular are, for example,-130 dBc/Hz at 1kHz offset and 19.2 MHz. Sand 9’s TCMO is the first MEMS oscillator to achieve this same performance but at a lower price along with the added benefits of MEMS versus crystal.”
“A significant additional benefit for communications applications is a superior ability to maintain synchronization,” Borkowsky says. “This leads to reduced packet loss in, for example, LTE products or superior ability to maintain GPS lock leading to enhanced end user experience.”
The technology also delivers a tuning range 10 times greater than quartz, enabling the capability to tune for more than aging, according to Borkowsky. And he provides an illustration: typical TCXOs have a pull (tuning) range of ±5 to ±10 ppm to account for initial frequency offset, thermal drift, and effects of aging. The Sand 9 TCMO offers a pull (tuning) range of ±50 ppm that provides RF designers with the additional flexibility to tune their system to avoid channel interferers. This helps accelerate RF development time and type approval.
Borkowsky points out that, in this example, comparisons of the ppm metrics do not relate to frequency stability over temperature discussed earlier, where low ppm is the target. “In this case,” he says, “we are looking at the pull or tuning range of the oscillator.”
“All this permits smart phone designers, for example, to tune their radio design around channel interferers, which greatly minimizes the number of exceptions needed and speeds time to market for new phones.” Borkowsky adds that because the phone has more available channels to use, end users are less likely to drop a call. “This also enhances the end user experience while providing the network operator with more efficient usage of their network,” he claims.
Reduced power consumption is always a goal since it has a direct impact on battery life, Si-Ware Systems CEO Dr. Haddara reports. In line with this, SiTime has rolled out the SiT8004, which it claims to be the industry’s lowest power high frequency oscillator by reducing power consumption by up to 66% to 6.7 mA. It is designed as a drop-in replacement for quartz and targets high performance networking, video, computing and storage applications, the company says.
As hand-held devices become smaller and incorporate more features, size becomes an issue. SiTime’s new SiT9105 device for networking applications is a MEMS based clock generator offering mixed LVCMOS and differential outputs in a single package. The 22-pin device measures 7.0 x 5.0 x 0.9 mm which, according to the company, reduces board area by up to 66% over comparable clock generators.
Another example of multifunctional MEMS oscillators is the DSC20XX series introduced earlier this year by Discera. Claimed by the company as world’s highest performance multiple output MEMS oscillators, the products exhibit 300 femtosecond RMS phase jitter and as low as ±10 ppm frequency stability. According to Discera, these oscillators are aimed at any application that uses multiple quartz crystals oscillators in order to reduce cost and complexity.
Cost and Product Comparisons
The following table provides representative comparisons of select MEMS oscillator products described in this overview and is based on the companies’ recent releases and data sheets.
In general, MEMS based oscillators can be produced at a lower cost than comparable quartz based devices. This is largely due to batch processing which allows the oscillator frequency to be set after the device fabrication steps. As with other MEMS technologies, higher production runs generally result in lower costs per device and this is expected to be the case with MEMS based oscillators.
Sand 9 comments that the move towards smaller size, combined with higher performance requirements, will result in quartz based technologies continuing an upward trend on the cost curve. Oscillators based on MEMS technologies will become less costly as volumes increase.
There are exciting market possibilities for MEMS oscillators in new product areas for consumer, military, telecommunications and automotive applications. This overview touches on only a few considerations relating to MEMS oscillator developments. This market segment is a continually evolving landscape as suppliers continue to roll out products with improved performance capabilities.
This article is a part of MEMS Investor Journal's ongoing market research project in the area of MEMS and non-MEMS based oscillator technologies. If you would like to receive our comprehensive market research report on this topic, please contact John Williamson at [email protected] for more information about rates and report contents.
Copyright 2011 MEMS Investor Journal, Inc.