editor's blog
Subscribe Now

Teasing Apart FBAR Loading and Temperature Effects

We hear stories of a not-so-distant future when we can wave our tricorder-like devices around and detect all kinds of substances that might be in the air. One of the ways sensors like this can work is by having a resonating body: when a substance adsorbs on the surface, it changes the mass, thereby changing the resonance frequency.

The problem is, however, that temperature also affects the frequency, and it’s actually pretty hard to calibrate that out of the system. Using a reference resonator or a complex software algorithm is possible, but, according to a team from Cambridge, Universities of Sheffield, Bolton, and Manchester in the UK, and Kyung Hee University in Korea, it makes things more complex and/or costly.

They’ve come up with a way of teasing the loading and temperature effects apart. It involves a two-layer structure: 2 µm of ZnO over 2 µm of SiO2. When they get this vibrating, they see two modes:

  • One with a fundamental frequency at 754 MHz and harmonics at 2.26 and 3.77 GHz
  • One with a fundamental frequency at 1.44 GHz, and the next harmonic at 4.34 GHz

The first mode comes from the resonance of the combined ZnO/SiO2 structure; its half-wavelength relates to the combined 4-µm thickness of the overall structure. The second mode results from the ZnO layer by itself, with a half-wavelength driven by the 2-µm thickness of this layer, although it’s also affected by the SiO2 load.

Both ZnO and SiO2 have positive coefficients of thermal expansion (CTE), so both layers get thicker as temperature goes up. But the longitudinal wave velocity goes up for SiO2 and down for ZnO. As a result, the frequencies move in opposite directions as temperature changes: roughly 79.5 ppm/K for SiO2 and -7 ppm/K for ZnO.

Given those as base numbers, it now becomes possible to deconvolve the temperature and loading effects of whatever it is you’re trying to sense.

This was, of course, a university project, although it looks like they will be open to commercializing it. You can get more details in the full paper, but it’s behind a paywall (actually, several; you can Google “Dual-mode thin film bulk acoustic wave resonators for parallel sensing of temperature and mass loading” and pick your favorite one).

Leave a Reply

featured blogs
Dec 1, 2020
If you'€™d asked me at the beginning of 2020 as to the chances of my replicating an 1820 Welsh dresser, I would have said '€œzero,'€ which just goes to show how little I know....
Dec 1, 2020
More package designers these days, with the increasing component counts and more complicated electrical constraints, are shifting to using a front-end schematic capture tool. As with IC and PCB... [[ Click on the title to access the full blog on the Cadence Community site. ]...
Dec 1, 2020
UCLA’s Maxx Tepper gives us a brief overview of the Ocean High-Throughput processor to be used in the upgrade of the real-time event selection system of the CMS experiment at the CERN LHC (Large Hadron Collider). The board incorporates Samtec FireFly'„¢ optical cable ...
Nov 25, 2020
[From the last episode: We looked at what it takes to generate data that can be used to train machine-learning .] We take a break from learning how IoT technology works for one of our occasional posts on how IoT technology is used. In this case, we look at trucking fleet mana...

featured video

Available DesignWare MIPI D-PHY IP for 22-nm Process

Sponsored by Synopsys

This video describes the advantages of Synopsys' MIPI D-PHY IP for 22-nm process, available in RX, TX, bidirectional mode, 2 and 4 lanes, operating at 10 Gbps. The IP is ideal for IoT, automotive, and AI Edge applications.

Click here for more information about DesignWare MIPI IP Solutions

featured paper

How to optimize an OpenCL Kernel for the data center using Silexica's SLX FPGA

Sponsored by Silexica

FPGAs are being increasingly employed as co-processors in data centers. This application note explains how SLX FPGA accelerates a Fintech design example, leveraging Xilinx’s Vitis Platform’s bottom-up flow, Alveo U200 accelerator card, and Vitis quantitative finance library.

Click here to download the whitepaper

Featured Chalk Talk

DC-DC for Gate Drive Power

Sponsored by Mouser Electronics and Murata

In motor control and industrial applications, semiconductor switches such as IGBTs and MOSFETS of all types - including newer wide-bandgap devices are used extensively to switch power to a load. This makes DC to DC conversion for gate drivers a challenge. In this episode of Chalk Talk, Amelia Dalton chats with John Barnes of Murata about DC to DC conversion for gate drivers for industrial and motor control applications.

More information about Murata Power Solutions MGJ DC/DC Converters: