Discussion on the design of bioelectric signal acquisition scheme based on SiC integrated technology

Human body information monitoring is an emerging field. People envision developing wireless electroencephalogram (EEG) monitoring equipment to diagnose epilepsy patients. Wearable wireless EEG can greatly improve the patient's activity space and eventually realize home monitoring through the Internet. Such wireless EEG systems already exist, but how to reduce their size to a level acceptable to patients is still a big challenge. This article introduces the use of IMEC's ​​SiC technology. Its development focus is to further reduce the size of the integrated EEG system and integrate low-power processing technology, wireless communication technology and energy extraction technology. An additional stacking layer with solar cells and energy storage circuits is added to the existing system, which can form a completely independent bioelectric signal acquisition solution.

Wireless bioelectronic communication systems will greatly improve people's quality of life in the future. To achieve this ideal, it is necessary to develop body-area networks (BANs) composed of small intelligent sensor nodes. The sensor nodes are used to collect important information about the human body and then send the information to a central intelligent node, which then sends the information to a base station through wireless communication. These sensor nodes can be designed and implemented with the help of 3-D stacked (System-in-a-cube, SiC) integration technology.

Small, low-power sensor/actuator nodes that form a body area network must have sufficient computing power and wireless communication capabilities, and should have integrated antennas. Each node must be intelligent enough to perform its assigned tasks, such as data storage and facilitating algorithm implementation, or even complex nonlinear data analysis. In addition, they should be able to communicate with other sensor nodes or central nodes worn on the body. The central node communicates with the outside world through standard telecommunications facilities such as wireless LAN or cellular telephone networks. Such a BAN can provide services to individuals, including monitoring and treatment of chronic diseases, medical diagnosis, home monitoring, biometrics, and sports and health tracking.

IMEC has recently achieved a technological breakthrough and developed a small three-dimensional stacked SiC system with a volume of only 1cm3. The first 3-D stacked prototype includes a commercial low-power microcontroller with 8 million instructions per second, a 2.4GHz wireless transceiver, several crystal oscillators and other necessary passive components, and a monopole antenna with a matching network designed by the user. Among them, both the microcontroller and the wireless transceiver use the most advanced energy-saving technology. The high integration of the system is achieved by stacking multiple layers with different functions along the Z axis through a technology called "3-D stacking". Each layer is connected to the adjacent layer through a double-row micro-pitch solder ball.

This universal stacking technology can realize any module combination. This low-power 3-D SiC system can be used in a variety of wireless products, from human body information (brain activity, muscle activity and heartbeat) monitoring to environmental data (temperature, pressure and humidity) monitoring, and finally used to form BAN. Due to its unique stacking characteristics, this technology can even integrate a specific sensor into a single layer to form a dedicated cubic sensor module.

Developing SiC is part of IMEC's ​​Human++ program, which envisions combining multiple similar SiC sensor nodes to form a BAN. The Human++ program combines wireless communication technology, packaging technology, energy extraction technology and low-power design technology to develop devices that can improve people's quality of life.

The success of such a BAN depends on how far we can extend the capabilities of existing devices. Therefore, several medical and technological barriers must be overcome. First, the battery-powered devices used today have a limited lifespan, and their service life must be extended. Second, the interaction between sensors and actuators should be amplified to accommodate new applications such as multi-physiological parameter measurement. Third, the devices should have a certain intelligence to store, process and transmit data. In addition, the functions of the devices must be extended to enable chemical and biological measurements. Finally, a thorough understanding of medical phenomena should be achieved.

Figure 1: IMEC's ​​2010 Technology Outlook.

Imec's extensive experience and know-how have enabled it to achieve new breakthroughs in a number of technological fields, creating opportunities to meet such challenges. Semiconductor scaling technology has led to the creation of smaller electronic devices with lower power consumption, making it possible to develop more powerful therapeutic and diagnostic devices.

With the development of microsystem technology, especially microelectromechanical systems (MEMS) technology, devices with both electronic and mechanical properties have been produced. The first application of MEMS technology is to develop energy harvesters for powering autonomous medical systems, such as energy harvesters based on thermal energy to electrical energy conversion, which can use body heat to generate micro energy. This source of energy is endless, so the system can always remain in operation and its life span is almost infinite. But the problem is how to prove that such devices can extract enough energy (i.e., at least 100 milliwatts) from the human body to support the operation of future systems. Another possible application of MEMS technology is for sensor and actuator systems, which are used to provide interfaces with the outside world and mixed-signal circuits around them. Finally, MEMS technology can also be used to develop new components (such as resonators) that can be used in ultra-low power (ULP) RF transceivers. ULP RF devices can be used to communicate between sensor nodes and wearable central nodes, with an average power consumption of 50μW.

Thanks to new packaging technologies, a large variety of complex systems (such as fluid biosensors, RF transceivers, microprocessors and batteries) can be integrated into a small device, making mobile wireless medical devices easier to wear.

Nanotechnology makes it possible to use small interconnected devices to enable direct interactions between the body's biological systems, such as cells, antibodies or DNA. New biosensors and implants may use this technology.

If a low-power processor architecture can be developed, the intelligence of sensor nodes will be further increased, so that the sensors themselves can perform more complex data processing. This requires us to design a ULP processor architecture (Uniform Instruction Set Processor Architecture and Data Memory Architecture) that can run biomedical applications. Today's biomedical applications generally require 20 million to 1 billion operations per second on non-optimized processors.

Finally, new design techniques can be used to effectively model, simulate and design the above applications.

Although the dream of humans wearing BANs will not become a reality until 2010 at the earliest, some related technologies have already emerged, the most famous of which is its application in the field of bioelectronics research. Bioelectronics is a field that contains unlimited opportunities. The combination of biological (or biochemical) reactions with electronic signal detection and amplification has produced new and exciting bioelectronic diagnostics. Similarly, using the connection between neural networks and computer chips at the micro level, pharmacological sensors can be developed and even neural electrical processors for medical and technological applications can be designed.

Human body information monitoring is another emerging field, such as the development of wireless electroencephalogram (EEG) monitoring equipment to diagnose epilepsy patients. The use of wearable wireless EEG can greatly improve the patient's freedom of movement and eventually enable home monitoring through the Internet. Such wireless EEG systems already exist, but how to reduce their size to a level acceptable to patients is still a big challenge.

Using IMEC's ​​SiC technology, the wireless EEG system can be integrated into a device with a volume of only 1 cm3. In this way, patients can wear a very comfortable wireless EEG device to do EEG. IMEC's ​​future development focus is to further reduce the size of the integrated EEG system and integrate its low-power processing technology, wireless communication technology and energy extraction technology. Adding an additional stacking layer with solar cells and energy storage circuits to the existing system may form a completely independent solution.