High-sensitivity piezoresistive cantilevers under 1000 Å thick

Abstract

Ultrathin, high-sensitivity piezoresistive cantilevers were constructed using vapor-phase epitaxy to grow the conducting layer. A fourfold reduction in thickness was achieved over the thinnest implanted piezoresistive cantilevers, allowing improved force or displacement sensitivity and increased bandwidth. In cantilevers 890 Å thick, the dopant is well confined to the surface, and the sensitivity is 70% of the theoretical maximum. A cantilever fabricated for high force resolution has a minimum detectable force of 8.6 fN/Hz in air. Additionally, the 1/f noise is shown to follow the relation proposed by Hooge [Phys. Lett A 29, 139 (1969)], increasing in inverse proportion to the number of carriers.

Design optimization of piezoresistive cantilevers for force sensing in air and water

“…The components of this model are well established, 2,10 but we verified the accuracy of the model by comparing it with the experimental data presented in Ref. 24 for a 90 nm thick epitaxial piezoresistor. The force resolution, integrated noise, and stiffness all agree to within 10% of the reported values, e.g., a force resolution of 0.5 pN is reported and we calculate a value of 0.56 pN.…”

“…Ion implantation causes damage to the crystal that must be annealed out, and it has been observed that ␣ decreases with the mean diffusion length ͑ ͱ Dt͒ of the dopant atoms during the anneal. For epitaxial piezoresistors, ␣ =10 −5 is typical 24 and we use this value in the presented analysis.…”

“…The number of carriers can be calculated from the dopant concentration profile and piezoresistor volume assuming a constant current density, 24 and for an epitaxial piezoresistor is N = nl pr wt pr . ͑16͒…”

On the design of piezoresistive silicon cantilevers with stress concentration regions for scanning probe microscopy applications

“…Piezoresistive cantilever detection has been found to have the disadvantage of less resolution when compared to optical detection [4]. The piezoresistive effect in silicon has been well documented in literature [5].…”

Fast on-wafer electrical, mechanical, and electromechanical characterization of piezoresistive cantilever force sensors

“…After this, many groups have developed systems and applications based on cantilevers with integrated piezoresistors for force or displacement sensing. These include the development of atomic force microscopy (AFM) probes, [5][6][7][8] probes for magnetometry, 9 the high force sensitivity achievement with <100 nm thin cantilevers, 10 the characterization of low force electrical contacts 11 and the study of the ultimate piezoresistive sensitivity at low temperatures. 12 We have previously presented the fabrication of cantilevers made of polycrystalline silicon using a commercial CMOS process flow together with integrated read-out a) Electronic mail: joan.bausells@imb-cnm.csic.es.…”