Publication date: 24 January 2012
MEMS manufacturing techniques have enabled the production of high performance and ultra-miniature timing components in small surface mount packages. The higher cost of these components however have encouraged designers to continue to use their old favourite: HC-49 crystals are often the highest components on the board.
Looking at the total cost of ownership, crystals such as Epson Toyocom’s QMEMS range are certainly no more costly than more traditional products, and offer enhanced performance and stability into the bargain. They are seeing increased adoption around the world though the UK is slower to follow. Is it time to reassess the choice of timing component?
Most commonly, microelectromechanical or MEMS systems are based on silicon, polymers or metals. Epson Toyocom pioneered the application of these manufacturing techniques to quartz crystal and launched its first QMEMS product in October 2006. Quartz is hard and lends itself well to precision manufacturing. It is also highly stable in response to changes in temperature, shock, vibration and exposure to chemicals. With these characteristics, the application of MEMS technology made substantial miniaturisation possible.
MEMS semiconductor manufacturing processes are based on wafer batch production, allowing productivity to be maximised and many different variants to be produced using the same tools. As size reduces, output can be increased by increasing the number of individual components per wafer. These tools can make much smaller quartz devices than is possible using conventional mechanical machining. These devices have proved extremely popular in hand held consumer electronics, due to their exceptionally small size and low power consumption – and are growing in popularity in electronics applications of all kinds.
The very precise fabrication improves stability and consistency. For example, photo etching technology enables a 20% reduction in the size of tuning fork crystals. Machine-processed tuning fork crystals designs are two dimensional constructions, which means that the smaller a tuning fork the greater the impedance, adversely affecting performance. Applying 3D MEMS technology can increase the overall surface area and helps hold down the increase in impedance.
As a result, the benefits of QMEMS extend beyond the production phase into the service life of the product. Due to the consistent and very high precision manufacturing approach, QMEMS crystals are very reliable and stable over time. Equivalent Series Resistance, for example, is stable even at very low drive levels, and is unaffected by exposure to solder reflow operations or ageing. SMD products are designed for reflow soldering, and will withstand exposure to temperatures of over 150®C providing the recommended reflow profile is adhered to.
QMEMs has led to Epson Toyocom capturing 24% of the global market, but its share of the UK market is much lower. This is probably because industrial electronic designs dominate the market in this country rather than the portable consumer electronics applications that dominate the volume, if not the value, of the world electronics market.
MEMS based quartz crystal timing technology offers a very competitive total cost of ownership, and better stability and performance than most alternatives. It is time that UK designers reassessed the value of this technology.
