A miniature one cubic centimetre 3D stacked system-in-a-cube (SiC), which comprises radio and digital signal processing (DSP) circuitry, will be used as the heart of a wearable, wireless electroencephalogram (EEG) currently under development at IMEC and the University Hospital Leuven, Belgium.
By actually wearing the device, patients can remain mobile while a electroencephalogram is taken and need no longer to remain in hospital for the procedure.
The SiC was developed as part of IMEC’s Human++ program, which envisions similar SiCs as sensor nodes constituting a body area network (BAN). The BAN will be used to gather vital body information into a central intelligent node, which in turn will communicate wirelessly with a base station.
This first 3D-stack prototype integrates a commercial low-power 8 MIPS (million instructions per second) microcontroller and a 2.4 GHz wireless transceiver, crystals and other necessary passives, as well as a custom-designed matched dipole antenna.
The high level of integration in a system was achieved through Z-axis, or ‘3D’, stacking of separate layers with different functionality. Each layer connects to its neighbouring layers through a dual row of fine pitch solder balls. The bottom layer has a BGA (ball grid array) footprint, allowing standard techniques for module mounting.
The tasks of the microcontroller unit range from adjusting sensor preamps and digitization to data interpretation, forward error coding and MAC (medium access control) implementations from low to medium complexity. The 12 bit microcontroller ADC (analog to digital converter) provides enough dynamic range for most sensors to be directly interfaced with the module.
Not only can EEG (brain activity), EMG (muscle activity) or ECG (heart activity) information from the human body be monitored, but also temperature, pressure, and humidity when the appropriate sensor is used. The unique stacking feature even allows designers to integrate a specific sensor into a single layer, resulting in an application-specific cubic sensor module.
Future developments will mainly focus on further size reduction and the integration of IMEC’s low-power processing, wireless and power-scavenging technology. By adding yet another layer to the cube that incorporates solar cells and energy-storage circuitry, the designers say that they will be able to create a completely standalone solution.