The Story of Timekeeping: From Pendulum Clocks to MEMS Oscillators (Part 3 of 3)

|by |

Imagine Galileo Galilei sitting in a church around the turn of the 17th century, his eyes fixated on a swinging chandelier. Galileo noticed something remarkable: no matter how wide or small the arc, the period it took for the chandelier to complete each swing remained the same. Moved by a breeze, the chandelier maintained a constant and reliable rhythm. This simple revelation would alter the course of timekeeping history.

Welcome to part 3 of our series on The Story of Timekeeping. Here, we move beyond the world of ancient timekeeping methods and the dawn of early mechanical clocks to discuss timekeeping based on the phenomenon known as isochronism-from pendulum clocks to modern MEMS oscillators.

The First Oscillators-Pendulum Clocks

Inspired by the chandelier oscillation and the principle of isochronism, meaning equal time, Galileo conceptualized the first pendulum clock. This theory was later modified and used to build the first successful pendulum clock by Christiaan Huygens in 1657.

Huygens' clock increased timekeeping accuracy by two orders of magnitude, from minutes to seconds a day. As a result, clocks finally earned the right to have second hands and became more consistent than the daily return of the Sun, which varies by as much as half a minute per day due to the equation of time. This advancement marked the conquest of time, as timekeeping devices became far more accurate than observation of natural phenomenon and more precise than the early mechanical clocks that had dotted the European landscape from the 13th century.

A rendering of an isochronous pendulum clock by Christiaan Huygens, according to Horologium Oscillatorium, published in 1673 A.D.

Navigating Time-The Balance Wheel and Spring

The need for portable timekeeping led to the invention of the balance wheel and spiral spring, another timekeeping advancement of Christiaan Huygens. These compact devices could fit into a pocket, bringing clocks to the high seas and beyond. The balance wheel, oscillating back and forth, governed by a spring, marked a new era of timekeeping by allowing timekeeping devices to operate in any orientation. The wheel and spring could replace the pendulum which is highly sensitive to the direction of gravity and will stop if tilted.

Huygens' inventions paved the way for new discoveries-his clock becoming the foundation of chronometry and the pursuit of accurate time measurement. Following his invention of the pendulum clock, Huygens attempted to develop a marine chronometer using a balance wheel and spring, but ultimately his early versions were not precise at sea.

Huygens' balance spring, invented in 1675 A.D., is still used in all mechanical wristwatches produced today.

In 1714, the British Parliament offered a longitude prize for accurately determining longitude at sea. Determining the location of ships at sea was extremely important for seafaring nations at this time. Having a naval advantage led to the ascendancy of the Royal Navy and British Empire.

This advantage required advancements in timekeeping accuracy and resiliency. Longitude can be calculated using a precise measure of time combined with astronomical observations. Therefore, crafting a precise timekeeper that could withstand the rough motion of the seas was paramount. It was John Harrison who eventually solved this challenge about 50 years later with his H4 chronometer which required accuracy to within two seconds per day, quite an achievement for a purely mechanical timekeeper.

The 20th Century-Advent of Modern Timekeeping

Fast forward to the early 1900s and the invention of the Shortt pendulum clock. This clock, accurate to within 1 second per year, kept time with two pendulums. The primary pendulum operated in a vacuum tank free of external disturbances. The second pendulum was attached to the clock mechanisms and was synchronized to the primary clock through electromechanical means. This design stresses a key requirement for maintaining accuracy of many timekeeping systems-the need for the oscillator time base to be disturbed as little as possible-highlighting the tradeoff between accuracy and resiliency.

The Shortt Synchronome Clock, invented in 1921 by William Hamilton Shortt, was used as a precise time reference into the 1940s.

Another new player in timekeeping enters the stage in the 1900s - the quartz crystal resonator. The invention of the quartz clock in 1927 was a leap forward in timekeeper stability, eventually making pendulum clocks obsolete as time references. The genesis of quartz timekeeping was the 1880 discovery of piezoelectricity by brothers Pierre and Jacques Curie. They observed that quartz crystals generate electrical charges when deformed by a mechanical force. Moreover, an electrical charge would lead to physical deformation and cause the quartz crystal to vibrate at a stable frequency.

With quartz crystals, watches became more accurate than ever before. Quartz clocks quickly became the new standard of time measurement and quartz crystals became ubiquitous in electronics, setting the pace for our increasingly digital world.

First commercial quartz wristwatch Astron Cal. 35A, Seiko, Japan 1969.

Silicon MEMS Oscillators-Micro Marvels of Modern Timekeeping

Despite their stability, quartz oscillators have limitations regarding their sensitivity to the operating environment. Changes in temperature, vibrations and accumulation of impurities impact their stability. This limits their integration into electronic devices leading to the adoption of alternatives such as microelectromechanical systems (MEMS) based oscillators.

Motivated by the shortcomings of quartz, researchers began developing the resonance properties of silicon MEMS structures in the 1960s. In the early 21st century, silicon MEMS oscillators were commercialized and are now the foundation of today's most resilient oscillators used to provide the heartbeat for many modern electronic systems.

SiTime is a pioneer in the timing market, developing products that offer several advantages over traditional quartz oscillators. These improvements have been achieved through MEMS technology, advancements in analog circuitry in the oscillator IC and timing systems expertise.

Due to the small size, mechanical structure, material properties and manufacturing processes, SiTime MEMS resonators have overcome the limitations of quartz crystals. Notably, the small mass and structure make them much less resistant to mechanical shock and vibration. The use of silicon material allows the use of novel designs and packaging techniques that make the oscillators much less immune to temperature change. Additionally, the semiconductor manufacturing processes that are used to fabricate SiTime MEMS, eliminate impurities and yield ultra-clean resonators that are resistant to factors such as aging that negatively affect stability. SiTime's groundbreaking work in precision timing has led to solutions that are both extremely accurate and resilient, setting new standards for stability, reliability and robustness.

The MEMS-based SiT1811 ultra-low power, low-jitter oscillator

The AI Revolution and Beyond-Solving Data Synchronization Challenges

As we venture into the age of AI, data synchronization emerges as a critical challenge. AI systems, with their voracious appetite for data-their speed, bandwidth and technological complexity-demand precision in timing to synchronize the data transmission. Here, MEMS oscillators shine, offering new architectural options that improve the efficiency of data processing. By ensuring precise synchronization, MEMS technology plays a pivotal role in the seamless operation of AI systems, edge computing and large-scale data centers.

As we continue to push the boundaries of possibility and advance timekeeping precision, accuracy and reliability, the role of MEMS in AI applications becomes ever more crucial.

To learn more about the history of timing, read our series on the Story of Timekeeping, or download the eBook.