Precision frequency references are required in many types of electronic devices such as cellular phones and other handheld devices. Crystal oscillators are typically used to provide the precision frequency reference in these electronic devices. However, crystal oscillators have several inherent disadvantages including large bulky size, fragility, and high cost. In addition, the size and cost of crystal oscillators is related to the resonant frequency so that as the frequency increases, the size decreases, and the cost and fragility may rapidly increase. As the size of electronic devices continues to decrease, the use of crystal oscillators becomes more problematic due to the size, fragility, and cost limitations.
Semiconductor oscillators have been a poor alternative to crystal oscillators and are generally unsuitable for use as a precision frequency reference due to excessive variation in the oscillating frequency, especially with changes in temperature.