Historically, InvenSense developed the first integrated dual-axis MEMS gyroscope for consumer electronics applications, and by 2006, its novel applications in consumer electronics (Nintendo Wii) products created very significant customer demand for similar products. ST did not enter the consumer MEMS gyroscope market until 2008, when it tried to catch up to InvenSense and target the growing consumer electronics market. ST did not develop a two-axis gyroscope for this market until 2009 and its three-axis gyroscope, at issue in this litigation, until 2010. InvenSense continues to innovate sensor technology with the first integrated six-axis gyroscope and accelerometer products introduced in 2011. Now they have the nine-axis, the first of its kind. 40% of ST's business is with Apple and now the word on the street is that INVN chips will be in Apple products - hence the more legal action by STM.
Keep in mind that patents granted prior to March 16 of 2013 were based on the "first to invent" standard rather than the current "first to file" standard. If STM did have a filed patent but INVN can be shown to have had a product prior to that date it would be "prior art" that would invalidate the STM patent.