Massively Parallel Scanning Probes Microscope with Digital Holographic Readout
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0961-O20-03
Massively Parallel Scanning Probes Microscope with Digital Holographic Readout Laurent Sache and Hannes Bleuler EPFL - LSRO, Lausanne, 1015, Switzerland
ABSTRACT Massively Parallel Scanning Probe Microscopy is an obvious path for enhancing the acquisition speed and the imaging range of current based-AFM metrology devices. Current experimental systems, based on active probes array, would reach their limits in density and hardware complexity. This paper presents a new approach with the promise to break several of these barriers. The key idea is readout of a Scanning Probes Microscope (SPM) array by an interferometer technique called digital holography which directly gives the cantilever phase information at each pixel of a CCD array. This means that no contact line to each individual SPM probes is needed, allowing us to reach very high density of probes. The phase information is available in a parallel form in real-time. Moreover, the digital holography optical setup (Digital Holography Microscope or DHM) needs in principle no expensive components, optical (or, to a large extent, mechanical) imperfections being compensated in the signal processing, i.e. in electronics. This gives the system the potential for a low cost device with fast and large readout capability. INTRODUCTION Today, a large part of tools used to interact with nanoscale structures are based on scanning probes technology founded with the invention of the scanning tunneling microscope (STM) by Gerd Binnig and Heinrich Rohrer of IBM's Zurich Lab in 1981. Today, the scanning probe microscope (SPM) technologies based on individual probe have reached their limit, principally by the slow data acquisition frames rate doe to their sequential readout. This last decade, great deals of efforts have been carried out for developing multiprobes SPM in order to increase range and acquisition speed. The concept is to make multiple cantilever probes on one chip which are controlled independently and coupled with a multiplexed cantilever detection method [1][2]. Developed in linear or in 2D configurations, manufactured starting from very diverse materials and coupled with a large range of sensors, the scanning probes devices extend nowadays their applicability to many different domains, starting from the observation to the direct interaction with nanoscale structures. However, an important limitation appears when using multiprobes SPM with multiplexed integrated sensors. Indeed, as density of probes increases, number of contact and interconnections wires increase and space for the leads decrease as much. Moreover, this contributes to enhance the complexity of the parallel electronics. With regards to these limitations, current studies and developments depict a limit up to 100 x 100 probes/mm2. This work is to our knowledge the first successful experiment which shows how to overcome this interconnection limit. The setup proposed here separates physically an entirely passive probes array, without any electrical correction, from massively parallel CMOS stand
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