1/F noise considerations for the design and process optimization of piezoresistive cantilevers

Citation
Ja. Harley et Tw. Kenny, 1/F noise considerations for the design and process optimization of piezoresistive cantilevers, J MICROEL S, 9(2), 2000, pp. 226-235
Citations number
25
Categorie Soggetti
Eletrical & Eletronics Engineeing
Journal title
JOURNAL OF MICROELECTROMECHANICAL SYSTEMS
ISSN journal
10577157 → ACNP
Volume
9
Issue
2
Year of publication
2000
Pages
226 - 235
Database
ISI
SICI code
1057-7157(200006)9:2<226:1NCFTD>2.0.ZU;2-X
Abstract
Piezoresistive cantilevers are limited by two major noise sources: Johnson noise, which is independent of frequency, and conductance fluctuation noise , which has a 1/f spectrum. The 1/f fluctuations of piezoresistive cantilev ers are shown to vary inversely with the total number of carriers in the pi ezoresistor, as formulated by Hooge in 1969, Therefore, while 1/f noise is reduced for large heavily doped cantilevers, sensitivity considerations fav or thin lightly doped cantilevers. Balancing these conflicting constraints produces optima for many design and processing parameters. For a cantilever with specified spring constant and bandwidth requirements, optima are iden tified far the beam thickness and Length, and it is shown that the legs sho uld be between 1/3 and 2/3 of the total length with a doping depth that is 1/3 of the beam thickness. Additionally, an optimal doping concentration is identified as a function of the cantilever volume and the measurement band width. Annealing reduces 1/f noise, but causes a loss in sensitivity due to dopant diffusion, and an optimal anneal is computed with a typical diffusi on length 10(-6) cm, The analysis, methods, and some of the conclusions of this paper are also applicable to other types of piezoresistive sensors.