Arindom Datta

Design, fabrication and characterization of metal embedded thin film thermocouples with various film thicknesses and junction sizes

Micro thin film thermocouples (TFTCs) can provide measurements with high spatial and temporal resolution. If these micro sensors can be embedded in metals, tremendous benefits can be achieved for real industrial applications. In this study, a novel batch microfabrication technique, based on the thin film transfer technique and wafer-scale embedding process, was developed to fabricate and embed thin film sensors into an electroplated nickel structure. To investigate the performance of metal embedded TFTCs and the effect of size on their temporal and spatial resolution, TFTCs with different junction sizes and film thicknesses were fabricated and characterized. The dynamic response time of the sensor on a metal substrate, as measured by the pulsed laser heating method, indicates that TFTCs have a significantly faster response than conventional thermocouples. The static response of the embedded sensor is found to be linear with temperatures up to 900 °C while the thermal sensitivity of the embedded TFTCs (film minimal thickness > 100 nm) matched well with that of a standard K-type thermocouple. As the junction size is incremented, no significant differences in the thermal sensitivity were observed, nevertheless the temporal resolution reduced. Thinner film thickness results in a faster response but reduced thermal sensitivity for embedded TFTCs.

Study on Embedding and Integration of Microsensors Into Metal Structures for Manufacturing Applications

Real time monitoring, diagnosis, and control of numerous manufacturing processes is of critical importance in reducing operation costs, improving product quality, and shortening response time. Current sensors used in manufacturing are normally unable to provide measurements with desired spatial and temporal resolution at critical locations in metal tooling structures that operate in hostile environments (e.g., elevated temperatures and severe strains). Microsensors are expected to offer tremendous benefits for real time sensing in manufacturing processes. Rapid tooling, a layered manufacturing process, could allow microsensors to be placed at any critical location in metal tooling structures. However, a viable approach is needed to effectively integrate microsensors into metal structures during the process. In this study, a novel batch production of metal embedded microsensor units was realized by transferring thin-film sensors from silicon wafers directly into nickel substrates through standard microfabrication and electroplating techniques. Ultrasonic metal welding (USMW) was studied to obtain optimized process parameters and then used to integrate nickel embedded thin-film thermocouple (TFTC) units into copper workpieces. The embedded TFTCs successfully survived the welding tests, validating that USMW is a viable method to integrate microsensors to metallic tool materials. Moreover, the embedded microsensors were also able to measure the transient temperature in situ at 50μm directly beneath the welding interface during welding. The transient temperatures measured by the metal embedded TFTCs provide strong evidence that the heat generation is not critical for weld formation during USMW. Metal embedded microsensors yield great potential to improve fundamental understanding of numerous manufacturing processes by providing in situ sensing data with high spatial and temporal resolution at critical locations.

Batch Fabrication and Characterization of Micro-Thin-Film Thermocouples Embedded in Metal

Micro-thin-film sensors are promising for in situ monitoring of various processes in that they can provide measurements with high spatial and temporal resolution. It is desirable to embed microsensors into metals, which are used as functional structures in most hostile industrial environments. However, the fabrication and embedding of these sensors into metals are very challenging. In this study, a batch microfabrication technique based on SU-8 patterning, electroplating, and wet etching of silicon is developed to fabricate and embed thin-film thermocouples (TFTCs) into electroplated nickel and to separate each sensor unit without the need of additional cutting. A dielectric multilayer (Al 2 O 3 /Si x N y /Al 2 O 3 ) provides insulation successfully for the embedded sensors from the nickel substrate and embedding layer. Study by using scanning electron microscopy and energy-dispersive spectroscopy line scan confirms that no significant interdiffusion occurs between different thin film layers after 10 h of annealing at 600°C. The embedded TFTCs provide a linear relationship between temperature and thermoelectric output. The sensitivity of the embedded sensors is almost identical to that of a standard K-type thermocouple. The fabricated TFTCs demonstrate a significantly faster response, approximately 46 ns, than conventional bulk thermocouples.

Metal Embedded Micro Sensors for Manufcaturing Applications

A novel batch production of metal embedded micro sensor units was realized by transferring thin film sensors from silicon wafers directly into nickel substrates through standard microfabrication and electroplating techniques. Ultrasonic metal welding (USMW) was used to integrate nickel embedded thin film thermocouple (TFTC) units into copper workpieces. The embedded TFTCs successfully survived the welding tests, validating that USMW is a viable method to integrate micro sensors to metallic tool materials. Moreover, the embedded micro sensors were also able to measure the transient temperature in situ at 50 mum directly beneath the welding interface during welding. Metal embedded micro sensors yield great potential to improve fundamental understanding of numerous manufacturing processes by providing in-situ sensing data with high spatial and temporal resolution at critical locations.

A Novel Batch Production Technique of Metal Embedded Thin Film Microsensors for Applications in Manufacturing

Effective monitoring and diagnosis of manufacturing processes is of importance in reducing operation costs, improving product quality, and reducing process time. If conditions of manufacturing tools are continuously monitored, problems can be detected and solved during the processing cycle, resulting in less tool damage, higher productivity, and less energy consumption. In-situ monitoring of the basic operating conditions (e.g. temperature and strain) of certain mechanical tools and components can be accomplished by placing microsensors in some critical locations. Thin film microsensors (e.g. thermocouple, strain gauge) have drawn considerable attention recently due to their small size, fast response and lower cost [1]. Since most tools and components in manufacturing process are metallic, metal embedded thin film microsensors are very attractive. A new batch fabrication technique based on electroplating and wet chemical etching of silicon has been developed. Microsensors were directly fabricated on an etch stop layer grown on silicon wafer. A multilayer dielectric is deposited to insulate sensor areas followed by seed layer deposition, and electroplating a thicker metal layer. After silicon wafer is etched out, the microsensors are transferred from silicon to electroplated metal substrate directly. After plasma etching of the etch stop layer, these sensors can be further embedded into another electroplated metal layer from the top after insulation by dielectric multilayer. Metal embedded strain gauge array was fabricated successfully. Thin film Ni/Cr strain gauges were fabricated on LPCVD silicon nitride layer grown on a 3-inch silicon wafer. Each strain gauge unit was insulated by Al2 O3 /PECVD Six Ny/Al2 O3 multilayer before seed layer deposition and electroplating a thick nickel layer on whole wafer. Si wafer was then etched out in KOH solution to transfer all microsensors to electroplated nickel layer. LPCVD nitride layer covering the sensors was dry etched and same multilayer dielectric was selectively deposited over the sensors except pad areas. These microsensors were finally embedded into another electroplated nickel layer leaving the pads uncovered for external connection. This process offers a novel way to realize batch production of metal embedded microsensors for use in hostile manufacturing environment.Copyright

Micro Thin Film Temperature Sensors Embedded in Metal Structures

This paper studies the fabrication and calibration of thin film temperature sensors embedded in metal structures. Thin film thermocouples have been successfully fabricated on various metal substrates and advanced embedding techniques have been developed to ensure sensor function inside metal structures. Thin film thermocouple was insulated with multiple thin film layers (Al2 O3 and Si3 N4 ) by e-beam evaporating and plasma enhanced chemical vapor deposition (PECVD). The sensors are calibrated. These embedded thin film sensors provide superior spatial and temporal resolution that is not possible with traditional sensors used in various manufacturing processes. This research is significant in a way that it provides a new and improved route for in-situ monitoring of manufacturing process.Copyright

Studies on Thin Films (Dielectric and Metallic) Constituting Micro Thermo-Mechanical Sensors Embedded in Metal Structures

It is of interest to obtain the thermomechanical response of tools, equipment, and structural components in a real manufacturing environment. Microfabricated thin film thermocouples and strain gages are attractive for their small size and fast response. It is novel and challenging to fabricate these sensors on metal substrate and finally embed them into location of interest. Consequently, the materials (dielectric and metallic) constituting the sensor need to be characterized and optimized properly for reliability. We present here results of characterization and optimization of materials making a thermomechanical sensor to be embedded in metal structure.Copyright