A bulk acoustic wave(BAW)-based sensor node for automotive wireless sensor networks

Abstract

The following paper presents a 2.1 GHz transceiver, which makes use of BAW resonators to replace the external quartz crystal and the external band select filter. It has been fabricated in a 130 nm CMOS process and has a power consumption of 5 mA. To derive the specifications for the transceiver the requirements of a TPMS have been taken into consideration.Der Einsatz von BAW-Resonatoren fü r drahtlose Sensornetzwerke im automotiven Bereich.Der folgende Artikel stellt einen 2,1-GHz-Transceiver vor, der anstelle einer externen Quarzreferenz und eines externen Hochfrequenzfilters BAW-Resonatoren einsetzt. Der Chip wurde in einem 130-nm-CMOS-Prozess gefertigt und hat einen Stromverbrauch von 5 mA. Um die Spezifikationen abzuleiten, wurden die Anforderungen an ein TPMS (Reifendruckü berwachungssystem) betrachtet.

Design issues of BAW employment in 3D integrated sensor nodes

“…Small sized shock-resistant BAW resonators are utilized for several purposes: carrier generation in transmit mode, local oscillator (LO) generation in receive mode, clock generation for the digital signal processing unit and lC's CPU, and as band select filters in the receive chain Flatscher et al 2008). In contrast to state of the art transceivers, the BAW based oscillators are directly resonating at the carrier frequency of 2.1 GHz, and therefore no phase locked loop is required.…”

“…Furthermore the electrical behavior of the BAW resonator can be modeled conveniently, as presented in (Flatscher et al 2008), where the BAW is shown to have an impedance of 2 kX at the parallel resonance frequency of 2.1 GHz. This property of the BAW turned out to be a major design issue, when connected to the transceiver die via TSVs, since this high impedance causes significant losses to the substrate.…”

“…Furthermore the sensor node should be as small as possible to avoid high force-gradients due to devicedeformation. Therefore, the system utilizes TSVs and advanced soldering techniques to result in a three level vertical chip stack for best compactness and highest robustness for pressure, inertia, and temperature sensing (Flatscher et al 2008). Figure 1 presents the TPMS wireless sensor node (WSN) including the 3D integrated chip stack.…”

“…To overcome temperature drift effects the temperature is measured and compensated by means of digitally controlled capacitors in parallel to the resonator (9 bit) in the range of -40°C through ?125°C. The same temperature compensation measures are applied to the BAW resonators used for RF-filtering Flatscher et al 2008). Therefore, the temperature of the BAW die needs to be determined exactly in every transmission cycle.…”

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

“…Additional benefits offered by a solidly mounted BAW resonator include extremely high mechanical robustness, higher quality factor (Q) than surface acoustic wave (SAW) devices or on-chip LC, small size, and lower temperature dependency as well as 10 times higher ESD robustness than SAW (5)(6) (7). Furthermore, the electrical behavior of the BAW resonator can be modeled conveniently, as presented in (8), where the BAW is shown to have an impedance of 2 kȍ if oscillating at 2.1 GHz. This property of the BAW turned out to be a major design issue, when connected to the transceiver die via TSVs, since such high impedance causes significant losses to the substrate.…”