3D-integration: Challenges and proposals

The first integrated circuits contained only a few transistors. Today, with the progressive miniaturization, complete systems can be realized on a chip. These are called system-on-chip. One example is the modern micro-controller which is the heart of many applications. They combine a processor, a memory and an analog-digital and a digital-analog converter that allows the evaluation of sensor data or the control of processes. Still, the integration of analog and digital circuits in a common semiconductor process is a major challenge in the design. While transistor sizes of digital circuits become smaller it is difficult to scale analog circuits since the transistor sizing depends on the driven currents. The integration of different sub-systems, therefore, often requires compromises in performance, power consumption, and design and manufacturing costs. Modern integration methods that combine several different IC in one package bridge this gap.