 Welcome to this presentation on Thelma 60's MEMS technology. ST Microelectronics is a leader in the field of micromechanical systems and is the only company to offer a full range of MEMS sensors and micro actuators, including motion sensors, microphones, environmental sensors, microfluidic devices, optical micro actuators, and piezo actuators. ST's MEMS are a success story with more than 11 billion MEMS devices shipped. Among these, more than 5 billion motion MEMS based on ST's proprietary Thelma technological platform have been shipped. An ST motion MEMS sensor is composed of three key elements. The first one is the sensor core, a micronsize transducer manufactured by a specific MEMS fabrication process called Thelma. The sensor is able to convert an acceleration or an angular velocity into a capacitive signal. The second one is a dedicated IC, which allows the output signal of the sensor to be read and converted into a digital or analog signal. The MEMS and the IC are combined together in a package and calibrated according to final product specifications. What does Thelma stand for? Thelma is an acronym for thick epitaxial layer for micro gyroscopes and accelerometers. Thelma technology is based on the fabrication of two wafers, a sensor wafer which embeds micromechanical components with sensing features, and a cap wafer which is used to seal the MEMS sensor in a hermetic environment by wafer level bonding. Wafer level device capping protects the micromechanical elements while the device is working. It enables the use of standard back-end technologies like testing, dicing, and packaging as well as ensures the reliability of the product over time. The Thelma fabrication process is a surface micromachining process based on the use of a thick layer of epitaxial polysilicon as the MEMS structural layer and silicon oxide as the sacrificial layer. A thin polysilicon film is used to design buried interconnects for signal rerouting and electrodes for out-of-plane displacement sensing. The fabrication process can be summarized as shown in the picture. Buried polysilicon interconnects are patterned on the MEMS substrate after an initial oxidation step. The sacrificial oxide layer is deposited on top of the interconnects and patterned to design mechanical anchors and electrical contacts for the MEMS structural layer. The epitaxial polysilicon layer is deposited and patterned on top of the sacrificial oxide using the DRIE silicon edge process. MEMS structures are mechanically released by the etching of the sacrificial oxide layer using a vapor HF edge process. After MEMS release, the device is encapsulated in a controlled atmosphere through a wafer level glass frit bonding process. The device cavity pressure set point is defined with values ranging from 0.1 to hundreds of millibar, according to the product specification. The Thelma fabrication process allows the manufacture of suspended mobile epitaxial polysilicon structures used for sensing motion through a capacitive detection principle. In-plane sensing is allowed by the design of in-plane epitaxial capacitors with rotor electrodes anchored to the mobile mass and fixed stator electrodes. Out-of-plane sensing is allowed by the design of out-of-plane capacitors with rotor electrodes built in the mobile epitaxial polysilicon mass and stator electrodes designed by the buried polysilicon layer. The capacitive sensing principle can be used for both acceleration sensing, accelerometer, and angular velocity sensing, gyroscopes. In this chart, an SEM picture of a MEMS device manufactured through the Thelma process is shown. A suspended epitaxial polysilicon mass is realized with flexure and mechanical anchors. Buried interconnects are shown. How can the Thelma technology platform evolve? Thelma 60 is a process option for Thelma technology, which allows the MEMS epitaxial polysilicon layer thickness to increase from 20 to 60 micrometers. What are the advantages of a thicker mass? There are different advantages. One, a thicker mass allows realization of in-plane capacitors with a higher area and a higher capacitance. This means sensors with a higher sensitivity. In other words, higher capacitance change under the same acceleration. In detail, Thelma 60 allows us to reach sensitivities in the order of PF per G versus FF per G sensitivities for traditional Thelma sensors. Two, as an alternative to the increase of sensitivity, a thicker mass allows us to put a device with a specific capacitance value in the same area, resulting in the shrinkage of the device itself. Three, a thicker mass also means a larger mass value. Which results in reduced sensitivity of the device to Brownian noise. Four, a thicker mass allows the design of devices with larger mass and higher sensitivity. In fact, sensitivity is inversely proportional to the sensor frequency and proportional to the mass of the sensor. A larger mass allows higher Z sensitivity. Before Thelma 60, high-end sensors were traditionally manufactured by bulk micromachining processes due to high sensitivity and higher mass requirements. In the bulk processes, sensing mass is built into silicon substrate by etching processes, allowing manufacture of thick MEMS layers. These processes are very complex and often result in high fabrication costs. Surface micromachining processes are traditionally used for consumer MEMS, where process simplicity is a key driver for high-volume manufacturing with high yields and reduced costs. Thinner device layer versus bulk processes is the reason why surface micromachining didn't allow the achievement of the performance required for high-end sensors. Thelma 60 allows us to realize thick MEMS mass devices without the cons of bulk micromachining processes and with the benefits of surface micromachining processes, like cost effectiveness, flexibility, smaller size and better yields. Thelma 60 bridges the gap between surface and bulk micromachining with the right requirements for high-end sensors and the key success factors of Thelma technology. A technological platform and architecture consolidated by the manufacturing of high volumes and the shipment of more than 5 billion units for consumer and automotive markets. ST controls the entire Thelma supply chain from design to FE manufacturing to BE and testing, a reliable and cost-efficient technology platform. ST is the first company to believe in the potential of Thelma MEMS technology, investing in the manufacturing of the first 8-inch MEMS fab in the world. But which are the main applications where Thelma 60 is making the difference? Implantable medical applications require very small and reliable high-sensitivity accelerometers to achieve ultra-low-power monitoring of the patient's activity and posture. Thelma 60 is the technological solution, combining the robustness and reliability with the miniaturization, the high-sensitivity and the cost-effectiveness. Moreover, it enables the supply of tested MEMS transducers in standalone packages, which can be directly connected, as typically requested in the implantable medical field, to the ultra-low-power custom ASICs designed by the end customer. Thelma 60 is the technology of choice to realize ultra-low noise and ultra-sensitive inertial sensors for oil and gas exploration by means of seismic methods. Traditional bulky electromechanical geophones can be replaced with MEMS sensors manufactured using the Thelma 60 process, resulting in better performance, cost-effectiveness, and space and weight savings. Thanks to Thelma 60, it is possible to partition the sensor system in the most convenient way, either embedding the mechanical MEMS transducer in the same small package with the readout electronics or keeping them in separate packages to be compatible with legacy solutions. With Thelma 60, it is possible to design high-accuracy, high-performance inertial sensors which meet the demanding requirements of stabilization and inertial navigation systems in industrial, avionics, and military applications, and at the same time are cost-effective with respect to traditional MEMS bulk technology. Thelma 60 is the disruptive MEMS process which enables the performance of traditional bulk micromachining technology using a cost-effective, reliable surface micromachining process. Sensors designed with Thelma 60 enjoy the benefits of ST's best-in-class manufacturing, like the 8-inch front end, the vertically integrated dual-source supply chain, and the reliable and cost-effective manufacturing machine sized for high-volume production and proved by more than 5 billion MEMS produced. Thelma 60 brings inertial sensor to higher levels. Thank you for your attention and visit us at www.st.com.mEMS.