PZT cantilever array integrated with piezoresistor sensor for high speed parallel operation of AFM $ Young-Sik Kim a,* , Hyo-Jin Nam a , Seong-Moon Cho a , Jae-Wan Hong b , Dong-Chun Kim a , Jong U. Bu a a Microsystem Group, Device & Materials Laboratory, LG Electronics Institute of Technology, Seoul, South Korea b School of Physics, Seoul National University, Seoul, South Korea Abstract In this research, the self-actuating high quality PZT cantilever with a piezoresistor was fabricated, and characterized for high speed AFM. The parasitic parameters inducing the electrical coupling between sensor and PZT actuator, was studied using simple equivalent circuit model of AFM cantilever. As a result of simulation, a new design was proposed to minimize the coupling capacitance between sensor and actuator by modifying the previous structure of cantilever described in [Appl. Phys. Lett. 72 (1998) 2340]. The fabricated PZT cantilever provided high tip displacement of 0.55 mm/V, has low leakage current, and enabled low voltage operation of AFM system. The optimized design at self-actuating PZT cantilever with a piezoresistor shows ®ve times lower coupling voltage than the current cantilever structure shown in [Appl. Phys. Lett. 72 (1998) 2340]. The measured resonant frequency was 73 kHz which was 100 times higher than that of conventional piezotube scanner. The piezotube scanner shows creep phenomena at scan speed of 180 mm/s scan speed, but the fabricated self-actuating PZT cantilever has a good scanned image even at 1 mm/s. Moreover, an array of 25 PZT cantilevers with piezoresistor that are spaced by 100 mm for parallel operation, was fabricated successfully. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Atomic force microscopy; PZT cantilever; Electrical coupling; High speed; PZT actuator; Piezoresistor 1. Introduction Atomic force microscopy (AFM) is a powerful tool for observing the surfaces with nanometer resolution. Recently, there has been an interest in increasing the throughput of AFM to implement AFM technology in industry such as a production line of semiconductor, scanning probe lithogra- phy, high-density data storage device and, etc. [1,2]. In spite of the striking advances in the technology of the instrument, the performance is still limited by slow speeds. To promote the scan speed of AFM, the thin ®lm piezoelectric actuators with high resonant frequencies have been integrated in the AFM cantilever in this research. Minne and coworkers had integrated an actuator with piezoelectric ZnO thin ®lm onto the piezoresistive cantilever. The integrated actuator improved the speed of the micro- scope by eliminating the need for an external z-axis actua- tor which had low resonant frequency, and the integrated piezoresistive sensor simpli®ed the operation of AFM [3,4]. They shows that the imaging bandwidth in the AFM system could be increased close to that of the cantilever resonant frequency. However, at high frequency operation, the ZnO cantilever with sensor and actuator, shows the serious elec- trical coupling problem between the actuator and piezo- resistor signals [4,5]. To eliminate the unwanted electrical coupling, Quate group proposed new measuring method [4], but this method needed additional components, such as lock- in ampli®er and ac bridge circuit, which introduced a com- plication in design and operation of AFM. Another method by Quate group was to modify the cantilever structure where bottom electrode of the ZnO actuator served as a grounding plane [5]. This prevented the signals that were applied to the top ZnO electrode from coupling capacitively to the piezo- resistor through the silicon substrate. However, this structure could not perfectly remove the coupling capacitance that was one of the major factor of coupling voltage between sensor and actuator signal. Moreover, the reported ZnO had low tip displacement and high leakage current. The maximum de¯ection of the ZnO cantilever was reported to be about 3 mm at several tens of applied voltage. Sensors and Actuators A 103 (2003) 122±129 $ This paper was presented at the 15th IEEE MEMS conference, held in Las Vegas, USA, January 20±24, 2002, and is an expansion of the abstract as printed in the Technical Digest of this meeting. * Corresponding author. Tel.: 82-2-526-4555; fax: 82-2-3461-3508. E-mail address: ysrevol@lg-elite.com (Y.-S. Kim). 0924-4247/03/$ ± see front matter # 2003 Elsevier Science B.V. All rights reserved. PII:S0924-4247(02)00311-4