A new process is developed to fabricate sub-50 nm current-perpendicular-to-plane (CPP) spin valve sensors. This processing technology relates to a feature reduction method using hard mask technique. The feature size is first reduced by an isotropic wet etch process of hard mask, and then transferred to CPP sensor by an ion milling process. Using this approach, the feature size can be reduced from above 100 nm determined by lithography technology to several nanometers. An etch back process is developed for the sensor via opening. Sidewall-free sub-50 nm CPP sensors have been successfully fabricated. The sensors are characterized through magnetoresistance measurements and show typical CPP characteristics. (c) 2005 Elsevier B.V. All rights reserved.