Design issues of BAW employment in 3D integrated sensor nodes

Abstract

In the field of wireless sensor node design a wide range of new potentials are opened by means of emerging 3D integration technologies. These technologies enable the design of highly integrated sensor nodes, but the designers face novel challenges, which specialized communications engineers are not familiar with. This work presents an advanced direct tire pressure monitoring system (TPMS) with an overall size below 1 cm3 applying through silicon vias (TSV) and points out two selected design issues arising due to this high level of integration. At first design issues caused by temperature gradients within the 3D integrated chip stack are presented. Multi physics simulations show that a systematical temperature measurement error is introduced by self heating, which would affect the communication performance if unconsidered. Furthermore the radio frequency (RF) characteristics of TSVs, focusing on their electrical efficiency, are investigated. In particular the behavior of TSVs for connecting a bulk acoustic wave resonator with an impedance of 2 kX at 2.1 GHz is evaluated in detail

Miniaturization of a Wireless Sensor Node by Means of 3D Interconnects

“…By means of this modification losses can be reduced to below 5% and therefore the TSV technology could be applied for required interconnect types of the wireless sensor node. In difference to the rectangular structures presented in (18), a reduction of the thickness of the substrate to 25 μm has only a minor impact on the efficiency.…”

“…The efficiency of a TSV is defined in (18) as the output power P o divided by the total electrical power P i resulting in…”

“…The efficiency Ș for the 3×10 μm 2 TSV is depicted in the solid line, where the losses at the operating frequency of 2.1 GHz can already be found by more than 70 %. In (18) the impact of three different parameters on the RF performance is investigated: the thickness of the isolation oxide, the conductance of the substrate, and the thickness of the substrate. Actually the electrical isolation properties of the tungsten filled TSVs turn out to have a major impact on the performance in RF applications.…”

3-D Integration and Through-Silicon Vias in MEMS and Microsensors

“…Fig. 40 shows a TSV 3-D integrated tire pressure monitoring system developed by Fraunhofer IZM (Berlin, Germany) [290]- [293]. The system has overall dimensions of 1.2×1.3×0.64 cm, and consists of a pressure sensor, an accelerometer, a microcontroller, memory, sensor signal processing circuits, and an RF transceiver.…”