Ž . Sensors and Actuators 86 2000 96–102 www.elsevier.nlrlocatersna Microfabrication of two layer structures of electrically isolated wires using self-assembly to guide the deposition of insulating organic polymer Andrew J. Black a , Paul F. Nealey b , Joseph H. Thywissen c , Mandar Deshpande d , Nada El-Zein d , George N. Maracas d , Mara Prentiss c , George M. Whitesides a, ) a Department of Chemistry and Chemical Biology, HarÕard UniÕersity, 12 Oxford Street Cambridge, MA 02138-2902, USA b Department of Chemical Engineering, UniÕersity of Wisconsin, Madison, WI 53706, USA c Department of Physics, HarÕard UniÕersity, Cambridge, MA 02138, USA d Motorola Inc. PCRL, 2100 E. Elliot Road, Tempe, AZ 85284, USA Received 16 November 1999; received in revised form 7 February 2000; accepted 21 February 2000 Abstract The fabrication of two layer structures of electrically isolated wire — crossed wire structures and a surface coil inductor — is described. The fabrication process utilizes the tools of soft lithography and incorporates two levels of self-assembly. The use of microcontact printing and patterned self-assembly of liquid polymers removes the need for registration of the insulating layer with the underlying layer as required in conventional lithography techniques. The performance characteristics of the surface coil inductor are measured and closely resemble those predicted by theory. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Soft lithography; Self-assembly; mCP; Surface coil inductor 1. Introduction The ability to fabricate multilevel structures of electri- cally isolated wires is essential to most micro systems that use electricity to compute, store information, actuate, or w x sense 1–5 . The fabrication of such systems requires several different layers of pattern transfer, with each of these layers correctly registered or aligned. The require- ment for registration adds to the complexity of the fabrica- tion process. Precise optical alignment of patterns becomes increasingly more difficult as the smallest aligned features become on the order of nanometers. We have been interested in developing non-photolitho- graphic processes for the fabrication of structures with feature sizes between 1 and 100 mm. These processes ) Corresponding author. Tel.: q 1-617-495-9430; Fax: q 1-617-495- 9857. E-mail address: gwhitesides@gmwgroup.harvard.edu Ž . G.M. Whitesides . Ž wx. which we call, collectively, Asoft lithographyB 6 have in common an elastomeric element that serves to transfer the pattern. Soft lithography is useful for rapid prototyping wx 7 of simple microstructures, non-planar microstructures, and microstructures containing materials not commonly wx used in microelectronics; examples include MEMS 8, wx w x w x optical waveguides 9 , stents 10 , microcoils 11 and w x microtransformers 12 , and simple microelectronic devices w x 13 . This paper describes the combination of microcontact Ž . w x printing mCP 14 with patterned self-assembly of liquid w x polymers 15–17 to create crossed wire structures with electrically isolated wires 10–100 mm in width, and a functional device — a surface coil inductor — with wires 100 mm in width. Because the patterned SAM directs the formation of the insulating layer — the polymer — by thermodynamic control, the combination of techniques eliminates two steps of registration that would be required to depositrpattern an insulating layer and vias in conven- tional semiconductor lithography. This method extends the general capabilities of mCP to make accessible multilayer 0924-4247r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0924-4247 00 00422-2