Typically, optical sensing techniques such as interferometric sensing or beam deflection are used. In recent years, we at IBM have been exploring two non-optical sensing schemes that have several advantages compared to the state-of-the-art.
One such sensing scheme is “electro-thermal” sensing, which was first conceived in the context of the scanning-probe-based data storage concept pursued at IBM [2003-1]. Electro-thermal sensing is based on heating and cooling of a micro-heater integrated into the body of a silicon cantilever while the cantilever moves closer or further away from the sample (Fig. 1). The motion of the cantilever results in a change in temperature of the micro-heater, which in turn translates into a change in the electrical resistance, which is then measured [2011-4, 2010-4, 2009-7, 2008-3].
We are also pursuing another scheme based on the use of magneto-resistance for deflection sensing. With this sensing scheme, the cantilever deflection signal is translated into a change in the magnetic field as seen by a magneto-resistance element (Fig. 2). Micro-magnetic simulations reveal that such a sensing scheme can achieve resolutions comparable to optical sensing techniques over MHz bandwidth [2011-11].
Figure 1. Electro-thermal sensing and modeling of sensing characteristics.
Figure 2. Magneto-resistance-based cantilever deflection sensing.