Discovery Platform™

What is a Discovery Platform™?
A Discovery Platform™ is a modular, micro-laboratory designed and batch fabricated expressly for the purpose of integrating nano and micro length scales and for studying the physical and chemical properties of nanoscale materials and devices. Discovery Platforms ™ will be standardized and packaged in a way that allows easy connections with external electrical, optical, and fluidic devices. The design and packaging will also allow direct access for a wide range of external diagnostic and characterization tools available at the Center for Integrated Nanotechnologies (CINT).

Why Discovery Platforms™?
Discovery Platforms ™ are born from CINT’s need to provide a user friendly environment where a wide range of scientists from backgrounds and disciplines can explore the interplay between microfabricated architectures and nanoscale materials and devices. Discovery Platforms™ provide the opportunity to explore issues around the central theme of nanoscience integration. CINT recognizes the inherent difficulty associated with mastering the broad range of fabrication skills needed to conduct experimental research that crosses the boundaries between nano/micro domains. We also recognize that crossing these boundaries requires a level of investment that can stifle multidisciplinary team’s participation in these important research directions. The NSF sponsored National Nanotechnology Infrastructure Network will provide important training opportunities for those who wish to learn new fabrication approaches needed to cross these boundaries. CINT recognizes the NNIN’s primary role in training and plans to offer Discovery Platforms ™ as a complementary approach where by the microfabrication step is effectively done by CINT and offered through the user program.

We anticipate that Discovery Platforms™ will serve a key role in building a coherent CINT user community. The consistency of experimental platforms should make it easier for various research scientists to compare results and build upon previous advances. Discovery Platforms ™ could also become a valuable teaching aid allowing students to explore the properties of nanoscale materials and learn about their connectivity with the micro and macroscale world.

When will Discovery Platforms™ be available?
The initial discussion of platform-based science and possible platform designs took place at the 3 rd CINT User Workshop, January 20-21, 2005. The workshop output was refined and an initial set has been identified (see below). Small teams are now working to define and prototype each platform. We anticipate that some of these platforms will be complete and available to users in the Spring of 2006 and others later in the year. CINT expects to continue developing new platforms in response to ideas from Users and CINT Scientists.

Cantilever Array Discovery Platform™

Contact: John Sullivan, jpsulli@sandia.gov, (505) 845-9496

Platform capabilities:
This platform is a multipurpose chip that is designed for experimenters wishing to perform research in the areas of nanomechanics, novel scanning probe technologies, chemical and biological sensing, magnetization studies, and physics of coupled mechanical systems. The platform is of the same physical dimensions as a standard AFM chip; therefore, it can be mounted on a standard AFM chip carrier and used in an AFM. Unlike an AFM chip, this platform has multiple cantilevers projecting from all edges, and it contains special test structures in the center. Some of the specific features of the platform are listed below:

Nanomechanics/Biomechanics: The platform includes arrays of polycrystalline silicon and silicon nitride cantilevers of different lengths and widths. As fabricated, the platform has openings in photoresist to permit the user to deposit their own material for testing. The cantilever structures are suitable for measurement of the modulus of unknown materials including nanostructured materials, for in situ film stress monitoring, and for studies of internal dissipation. In addition to cantilever structures, torsional oscillator structures and cantilevers with built-in in-plane force sensing are available. Torsional structures permit mechanics testing under shear loading conditions; the cantilevers with in-plane force sensing are suitable for probing soft or biological specimens. Located in the center of the platform chip are a series of in-plane load cells. These structures permit tensile or contractile loading to be performed on soft or biological specimens. In addition, a special mechanics structure is supplied that consists of a bridge over a silicon nitride membrane. The membrane can be pre-cracked to enable fracture mechanics testing. These structures also have Bosch-etched clearance holes completely through the chip, enabling the user to perform in situ TEM measurements simultaneous with mechanical loading.

Novel scanning probes: Many of the cantilevers emerging from the edge of the chip would be suitable for advanced or experimental scanning probe technologies. Some select cantilevers are pre-patterned with openings in photoresist to enable the user to deposit metal lines down the cantilever for resistive heating, thin film resistor thermometry, scanning electrical conduction measurements, etc. Other cantilevers have an opening in photoresist at the extreme tip to enable the deposition of a magnetic film or magnetic nanoparticles for magnetic force sensing. The cantilevers are fabricated from both polycrystalline silicon and silicon nitride with a variety of lengths and widths (hence, a range of force constants).

Physics and sensing with arrays: Several regions of the chip have dense and sparse arrays of similar-sized cantilever oscillators of both polycrystalline silicon and silicon nitride. These arrays can be functionalized and used for chemical or biological molecule sensing. In addition, the coupled arrays can be used for physics studies of collective behavior associated with coupled mechanical oscillators.

Magnetization studies: In addition to cantilevers that allow the user to deposit magnetic particles at the tip, the platform contains spring-suspended plates that are suitable for supporting a user-deposited material for magnetization testing. Polysilicon resistors for thermometry, polysilicon electrodes for capacitance sensing of displacement, and a Bosch-etched clearance hole for optical detection of displacement are also provided.

Other: A variety of other structures are provided, including arrays of cantilevers over silicon for measurement of surface adhesion forces, bridge structures that may be probed by nanoindentation to permit testing of materials at high stresses and strains, and sacrificial beams and bridges fabricated out of silicon dioxide that enable the user to deposit and test their own free-standing material.

Fundamental Science Questions: Some of the fundamental science questions that could be addressed by this platform include:

What are the deformation mechanisms (elastic/plastic behavior) in nanoscale and nanostructured materials?

What is the collective behavior of a system of oscillators when the interaction is increased or defects or mechanical noise are introduced?

What is the response of the cytoskeleton of a cell to local compression and traction & how does the cell accommodate the stress?

What controls energy dissipation in small crystalline and amorphous mechanical resonators?

What is the magnetization of collections of small particles near the superparamagnetic threshold?

What are the attractive and repulsive forces at surfaces between dissimilar materials?

What is the spatial variation of thermal conductivity/magnetization/modulus/etc. in nanostructured materials?

Design technologies:
The plan is to use a standard SUMMiT V™ process or a SwIFT™ process and have the fabrication performed at the MDL at Sandia. The SwIFT™ process uses nitride layers that would be of great utility for our platform. I have not heard back from Harold Stewart on whether the SwIFT™ process will be as available to users as the current SUMMiT V™ process already is. In addition to the standard process, we will need deep reactive ion etching (Bosch etching). The decision of whether some small fraction of the die should be pre-released for the users has not been decided (for many users, they will need the die in the unreleased form to permit some post-fabrication processing prior to their testing).

Electrical Transport and Optical Spectroscopy Discovery Platform™

Contact: Richard Averitt, raveritt@lanl.gov, (505) 667-1644  

Platform capabilities:
The electrical transport and optical spectroscopy (ETOPS) Discovery Platform™ will enable fundamental investigations of the optical, electronic, and transport properties of a wide variety of nanomaterials. ETOPS seeks to provide a well-characterized means of interfacing with the nanodomain while simultaneously offering considerable versatility for optical and transport measurements. In addition, ETOPS will be compatible with other measurement techniques including scanning probes such as AFM, STM, NSOM, electron beam characterization tools such as TEM and SEM, and cryostats and magnetic fields. Additional on-chip capabilities include temperature measurement and signal amplification. For maximum versatility this 2 X 2 cm platform is divided into four 1 X 1 cm quadrants as described in the following:

Quadrant I: This quadrant contains pads and interconnects which feed into a 100 X 100 micron region that is unpatterned except for e-beam alignment marks. This quadrant is reserved for user specialization offering, for example, the possibility of pattering nanoelectrodes. This quadrant (and the others) will also have temperature sensors and other discrete components such as JFETs to enable on-chip amplification. This quadrant should have broad appeal even to device researchers as it provides an excellent starting point for specialization.

Quadrant II: This quadrant is designed to offer a suite of electrodes for a variety of transport measurements coupled with backgating which will provide the option for electrostatic doping studies. There will be 6 different 100 X 100 micron regions. Three of these will have parallel electrode arrays with (a) 0.35, (b) 1, and (c) 3 micron gap spacing between the electrodes. The other three regions will have 4 terminated electrodes where the gap is 0.35, 1, and 3 microns for the three regions.

Quadrant III: This will be similar to quadrant II in terms of the electrode structure. The difference is that there will be no backgating – rather this quadrant will have a silicon nitride membrane window in the active regions which will enable, for example, simultaneous transport and electron beam interrogation of the sample. In addition, sensors (e.g. temperature, Hall, etc) will be incorporated into the active region allowing for further measurement / monitoring of the nanomaterials.

Quadrant IV: This quadrant is designed for broadband optical spectroscopy measurements, and other optical measurements as well (e.g. Raman, ultrafast, etc). Two options are available. The first is having a silicon nitride membrane window > 5 mm X 5 mm for transmission experiments. The second is two have an interdigitated grid structure (grid spacing about 200 microns) to enable optical measurements coupled with electrostatic doping (a la Basov).

Fundamental Science Questions: Fundamental science questions to be addressed by this platform include:

• Electronic transport in molecules, nanowires, and composite nanostructures (e.g. semiconductor or metal nanoparticle arrays)
• Transduction of molecular scale events to measurable electronic or optical signals
• Electrostatic doping of organic thin films and composite nanostructures
• Correlation studies of nanostructure and nanoscale-to-microscale functionality

Issues:
How large can the Si 3N 4 membrane window be made while maintaining structural integrity?
How low in temperature can ETOP go without freezing out the carriers in the device rendering it inoperable?

Finally, ETOPS can be used in the 2X2 cm format, or it can be diced into four individual pieces if so desired. The quadrant III structure can be further diced down into ~ 3 mm X 3mm pieces so that the active electrode structure can be incorporated into, for example, a TEM while maintaining electrical contact.

Design technologies:
The goal is utilize Summit design rules using with two or three mask levels. The fabrication of this platform will involve SiO 2 deposition, putting down either aluminum or polysilicon lines, and growing Si 3N 4 films followed by KOH back etching of the substrate.