NIRT: Heterogeneous Integration of Nanowires for Chemical Sensor Arrays

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Intellectual merit:"Electronic nose"chemical sensor arrays are used to detect trace analytesin complex mixtures,and are important for environmental,biomedical,process control,andsecurity-related applications.Scaling chemical sensors to nanometer dimensions will openunprecedented opportunities for implementation of electronic nose arrays in and-held devices,remote monitoring,robotics,medical diagnostics,sensor dust,and other novel applications.To do this,we must create low cost,low power,massively parallel arrays of chemically diversenanosensors and integrate them with on-chip data processing.The proposed project will bringtogether an interdisciplinary team from three institutions to work on the fundamental problemsconnected with this goal.The project combines the expertise of chemists in nanosensorsynthesis,physicists in materials and device characterization,electrical engineers inheterogeneous integration and test circuit design,and computer scientists in the design,fabrication,and testing of novel low-power circuit architectures.While this project focusesspecifically on nanosensor arrays,the problems it addresses are generic to the integration ofmany different kinds of functional nanoscale objects into silicon-based circuits.Our approach builds on an existing knowledge base of chemical sensor array platforms anddata analysis methods,to which our team brings some unique new materials and techniques.Mallouk and Semancik have developed a method for incorporating chemical sensor "stripes"intotemplate-grown metal nanowires.These nanowires connect the lithographic length scale (micronnanowire length)with the nanoscale (30-300 nm diameter and stripe length).The synthetictechnique allows the chemical nature of the sensory material to be quite diverse.We will focuson three different sensor platforms -chemoresistive metal oxides,intrinsically conductingpolymers,and conductive polymer composites -which should provide excellent orthogonality insensor arrays.The physical properties of the sensory materials and of the nanowires will bestudied using test structures devised by Evoy and Semancik,focusing in particular on the thermaland temporal signatures of the nanosensor response.The synthesis and physicalcharacterization of the nanosensors will be tightly coupled so that a molecular-levelunderstanding of signal transduction and scaling effects can guide the optimization of the sensors.Mayer and Evoy have developed an electrofluidic alignment technique for placing nanowires inlithographically defined circuits.This will be a powerful tool for parallel heterogeneousintegration of the nanosensors into large arrays.Issues of yield,device density,and testing/logiccircuit integration will be addressed through a combined approach of simulation and experiment,in collaboration with Irwin and Narayanan.Finally,Irwin,Narayanan,and Mayer will designand test a CMOS sensor processing fabric that efficiently controls the duty cycle of sensoroperation and processes the array response locally.Feedback between device/circuit testing andnanosensor synthesis and characterization will tie the whole project together.Broader impact:The NIRT team will apply its diverse scientific background in educationand outreach activities at the graduate,undergraduate,high school,and K-8 levels.The researchprogram has a strong element of mentoring of women,minorities,undergraduates,and high schoolstudents.It will also provide a cross-disciplinary experience for graduate students throughexchange with partner laboratories.In each summer of the program,NIRT faculty and studentswill team with Penn State Action Potential staff to develop a series of 5 th -8 th grade science campson different current topics.The unique aspect of these camps is that they bring elementary andmiddle school teachers together with students,so that teachers can use new curricular material ina practical environment.NSF funds will be used to support the participation of teachers frombeyond our local area,to increase the geographic and minority impact of the outreach program.