Four years ago, the category new MEMS, i.e. three-axis gyroscopes and pico projectors for consumer electronic and mobile handsets, did not exist. This year, analysts IHS iSuppli believe this sector will grow over 157%.

As smartphones and tablet PCs shipments increase, the revenue for MEMS devices could reach $457.3milion, more than doubling 2010's sales of $177.6million. Three-axis gyroscopes alone are expected to reach 200million pieces in 2011.

Although it may be feeling sidelined by the new contender, the established MEMS market, i.e. accelerometers and single- and dual-axis gyroscopes, is still strong and should grow 10.4% in 2011. At the Globalpress Summit Alissa Fitzgerald, board member, the MEMS Industry Group (MIG), enthused about the CAGR of 10.7% from 2009 to 2014 and identified mobile phones as responsible for generating the strongest demand growth. MEMS revenue to the mobile phone segment is expected to rise to $3.73billion in 2014, tripling 2009's $1.3billion. Other areas identified by MIG are gaming, laptop and tablet PCs, automotive, biomedical and industrial.

There is also the MEMS digital microphone subset, which is expected to achieve an annual growth rate of over 40%, with close to 450million units by 2014. Akustica was a pioneer of the digital microphone in 2006 and remains the sole supplier of monolithic MEMS microphones. As microphones are increasingly used in tablet PCs and gaming applications as well as the handset and laptop market, companies like STMicroelectronics have entered the acoustic sensor technology market.

Microphones

At the Globalpress Summit, Akustica introduced its AKU230 digital CMOS MEMS microphone (see EPN, May, front cover story). The 0.7mm² integrated device (Figure 1) can be used in a microphone array on camera modules in laptop PCs, by virtue of its user-selectable right or left channel option. The monolithic CMOS technology integrates the mechanical function of the microphones and sensors with analogue and digital electronics in a single chip that can be located anywhere on a board; immune to EMI and RFI which also improves voice capture. At 3.76x4.72x1.25mm, it is 30% thinner than the company's previous digital microphones. It has a -26dBFS±2dB sensitivity and a typical SNR of 56dB. Power supply rejection is -57dBFS.

Competing in the MEMS microphone market, STMicroelectronics introduced two digital MEMS microphones. The MP34DB01 and MP45DT02 microphones are for mobile phones and portable computers as well as emerging application which also require a voice input, such as tablet PCs and gaming devices.

The microphones use acoustic sensor technology jointly developed by STMicroelectronics and Omron. The microphone consumes less power than traditional condenser microphones for a longer battery life. Arrays of multiple microphones provide active noise and echo cancelling. Beam forming isolates a sound and its location to enhance mobile phone performance.

The MEMS microphones also exhibit high temperature stability after reflow. The MP34DB01, for example, (Figure 2) is claimed to be the only device available with hi-fi audio bandwidth, delivering flat frequency response in the 20 to 20,000Hz audio band, coupled with a SNR of 62dB and power supply noise rejection of 70dB. The 3x4x1mm package has an acoustic port hole on the bottom of the package, specifically for mobile phone use. The microphone can be mounted on the rear of the PCB for slimmer designs while obtaining a short acoustic path to the microphone. The MP45DT02 is a top port device, measuring 3.76x4.72x1.25mm for laptop and tablet PCs. SNR is 58dB.

 

MEMS-based timing

In Santa Cruz, SiTime's Piyush Sevalia explained how the company is concentrating on MEMS-based silicon timing. For tablet PCs and e-book readers, the company has announced the SiT8003 low power MEMS oscillator, which is 30% thinner than quartz and which is 10 times more robust to shock and vibration. According to Sevalia, over 200million tablet PCs and e-book readers are expected to ship by 2014, many with the company's low power, programmable MEMS oscillators as the timing reference.

The programmable devices can be configured to drive different devices within a tablet PC or e-book reader. For example, the SiT8003AC-12-18S-26.00000 configuration can be used for the applications processor and USB 2.0 transceiver. The -12-33S-14.31800 version can be used for the platform controller hub chip; the -12-33S-22.57920 can be used for the HDMI SoC while the -12-33S-24.57600 can be used for the audio codecs and the -12-33S-27.00000 can be used for the camera module.

Frequencies between 1 and 110MHz can be configured with accuracy to five decimal places. A customised clock frequency can be used for over-clocking or more economical testability. Configurable operating voltage is 1.8, 2.5, 2.8 or 3.3V.

The MEMS oscillator is delivered in a small 2.5x2mm package and consumes just 3.5mA in active mode and less than 5µA in standby. It offers ±25PPM frequency stability over -20 to +70°C. Controlling the rise and fall times of system clocks reduces system EMI and can meet environmental compliance without design changes.

Figure 1: The world's smallest, integrated MEMS device, the AKU230 microphone is from Akustica.

Figure 2: The MP34DB01 from ST Microelectronics is qualified for mobile phone manufacture.

Figure 3: The SiT800 MEMS oscillator from SiTime offers configurable control.