Figure 1: MTMC facility for photothermal diagnostics of microdevices.
It is used for thermometry with temporal resolution of 1 ns and, using
the near-field optical path, spatial resolution near 50 nm.
Facilities
Microscale Thermal and Mechanical Characterization Laboratory (MTMC)
The engineering community is developing a wealth of promising microstructures, including multilevel copper interconnects, monolithically-integrated fluid valves, thermal radiation detectors, and smart-power circuits. The thermal and mechanical properties of these microstructures, which can strongly influence their performance and reliability, are rarely the focus of rigorous experimental study. This motivated Stanford University Mechanical Engineering faculty K. E. Goodson and T. W. Kenny to found the MTMC Lab, which develops experimental science for microstructures within a department that leads in heat-transfer and applied-mechanics research.
Professor Goodson's group develops the thermal characterization experiments
at MTMC, many of which use high-speed photothermal diagnostics at the facility
shown in Figure 1. Temperature fields and thermal properties in electronic
microstructures are captured using near-field and far-field optics. The
far-field system uses rotating mirrors to direct laser radiation onto microdevice
surfaces with spatial resolution finer than 1 µm. The near-field
system scans an optical fiber about 5 nm above the surface of the sample
to overcome the diffraction limit and achieve spatial resolution near 50
nm. Related facilities at MTMC include temperature controllers, GHz signal
acquisition equipment, and an electrical probe station.
Figure 1: MTMC facility for photothermal diagnostics of microdevices.
It is used for thermometry with temporal resolution of 1 ns and, using
the near-field optical path, spatial resolution near 50 nm.
The mechanical characterization activities at MTMC are lead by Professor T. W. Kenny, whose group develops and studies a variety of novel microsensors and actuators. Measurements of mechanical properties and noise spectra are performed on detectors and cantilever structures using a high-frequency laser vibrometer and a closed-circuit helium-cooled cryogenic stage.
The activities at MTMC benefit strongly from the extensive micromachining facilities available on campus, both at the Stanford Nanofabrication Facility (SNF) and Ginzton Laboratory. SNF includes a 10,500 square foot, ultra-clean laboratory that is specifically engineered to support research on semiconductor devices and compact sensors and actuators. Modern processing equipment includes 2 ion implanters, 24 furnaces, PECVD and LPCVD tubes, 8 plasma etchers, and an ASM reactor.
IBM Thermal Simulation Resources
The experimental data are compared with predictions obtained using computers donated in 1997 by IBM Corporation. The donated equipment includes three IBM RS/6000 43P Model 240 dual processor workstations, each with a 9 GB hard drive and 500 MB of RAM. The workstations are used for three types of heat transport simulations, whose regimes of validity and applications are summarized in Figure 2. The Peierls-Boltzmann transport equation for phonons, which are the quanta of lattice vibrational energy, is integrated using finite-difference and line-of-sight techniques. Projects 1 and 4 in this booklet incorporate the transport physics into modified forms of the classical heat-diffusion energy equation, which support practical finite-element electrothermal simulations of transistors and other microdevices. The computational resources also support a growing effort in atomistic simulations for nanoscale devices and processes.
Figure 2: Hierarchy and applications of simulations that investigate energy transport in micro- and nano-structures. More information is provided in the project summaries.
Microscale Thermosciences Teaching Laboratory (MTTL)
There is a growing demand for heat-transfer expertise to aid with the design of microfabricated transistors, sensors, and actuators for the IC and MEMS industries. However, the mechanical engineering curriculum provides students with little exposure to the thermal phenomena and thermal diagnostics tools relevant for microdevices. To help remedy this situation, we are developing the Microscale Thermosciences Teaching Laboratory (MTTL), which features conduction and convection experiments performed on electronic microstructures. The primary goal is to teach classical conduction and convection through experiments on high-technology microdevices of relevance for silicon valley companies.
The MTTL provides a unique environment for undergraduate students to study microscale heat transfer as part of the core curriculum. Equipment includes the two high-resolution electrical probe stations shown in Figure 3, each of which offers a microscope, camera, and a video monitor. Students can visualize, electrically probe and heat, and perform electrical-resistance and thermocouple thermometry on microdevices fabricated at the Stanford Nanofabrication Facility and at local companies. Details about the specific measurements are provided in the teaching pages. Because the probe stations and visualization equipment are applicable to a broad variety of microdevices, the possibilities for new teaching laboratories using the same facilities are unlimited.
Figure 3: Probe stations and video equipment used by undergraduate students as part of the core mechanical engineering curriculum at Stanford University. The equipment makes possible conduction and convection experiments on interconnects and on thermally-actuated microvalves, as discussed the teaching project.