This is a great process achievement by SiTime. They have managed to cure the problem of MEMS oscillators over temperature at the source—the MEMS itself. Kudos to the process engineers!
SiTime Corporation has introduced the TempFlat MEMS. Until recently, all MEMS oscillators used compensation circuitry to stabilize the output frequency over temperature. This new design eliminates temperature compensation, resulting in higher performance, smaller size, lower power and cost.
The basic architecture of a MEMS oscillator combines a MEMS resonator die together with an oscillator IC. As shown on the left side of the diagrams below, SiTime has developed different types of MEMS resonators for different applications needs. The output frequency, which can range from 1 Hz to 625 MHz depending on the specific device, is configured by using a phase locked loop (PLL) that is located on the analog oscillator die. On-chip one-time-programmable (OTP) memory is used to store the configuration parameters. Output drivers usually offer configurable drive strength, for best matching of transmission line impedances and to reduce system EMI.
For more detail: SiTime’s MEMS Resonators: An alternative to Quartz