James Bustillo

DNA Transport by a Micromachined Brownian Ratchet Device

We have micromachined a silicon-chip device that transports DNA with a Brownian ratchet that rectifies the Brownian motion of microscopic particles. Transport properties for a DNA 50-mer agree with theoretical predictions, and the DNA diffusion constant agrees with previous experiments. This type of micromachine could provide a generic pump or separation component for DNA or other charged species as part of a microscale lab-on-a-chip. A device with reduced feature size could produce a size-based separation of DNA molecules, with applications including the detection of single-nucleotide polymorphisms.

Embedded interconnect and electrical isolation for high-aspect-ratio, SOI inertial instruments

A new technique for providing both electrical isolation and embedded interconnect to SOI-based, single crystal silicon, inertial sensors is described. This technology allows fabrication of high-aspect-ratio, in-plane, capacitive sensors with improved sensitivity suitable for integration with on-chip electronics. Various 45 /spl mu/m-tall MEMS devices with electrical isolation from the silicon substrate and embedded interconnect have been fabricated and tested. The embedded interconnect and electrical isolation enable truly integrated high-aspect-ratio MEMS sensors, and alternatively simplifies packaging in monolithic two-chip approaches. By extending the demonstrated technique to aluminum interconnect, only two additional masks are required to convert a CMOS process into a fully integrated MEMS technology at the incremental cost of an SOI starting material.

Process technology for the modular integration of CMOS and polysilicon microstructures

Modular fabrication of polysilicon surface-micromachined structures after completion of a conventional CMOS electronic process is described. Key process steps include tungsten metallization with contact diffusion barriers, LPCVD oxide and nitride passivation of the CMOS, rapid thermal processing for stress-relief annealing of the structural polysilicon film, implementation of a sacrificial spin-on-glass planarization, and the final microstructure release in hydrofluoric acid. Modularity of the process enables independent modification of either the CMOS or the microstructure process sequences. This technology is used in the fabrication of various types of sensors and actuators.

Differential transport of DNA by a rectified Brownian motion device

An interdigitated electrode array (IDEA) device has been designed and used to transport DNA based on a Brownian ratchet mechanism. This migration is produced by the periodic formation of an asymmetric sawtooth electric field in the device. Oligonucleo tides of 25, 50, and 100 bases in length were tested using two different array geometries. DNA transport as a function of DNA size, electric field frequency, and array geometry is shown to be in qualitative agreement with theory. Such a device could provide for DNA separations over a broad size range, and can be readily scaled as a component in a microfabricated DNA analysis system.

Flow measurements in a micromachined flow system with integrated acoustic pumping

In this paper a general scheme for the realization of micromachined flow systems with integrated fluid pumping is introduced. Microscopic channels are formed at the interface between an etched glass cap and a silicon micromachined flexural plate wave (FPW) device. The FPWs excite an acoustic field in the fluid that occupies the channel, and the acoustic field in turn drives fluid flow. The flow driving mechanism is acoustic streaming, a nonlinear acoustic phenomenon in which a finite-amplitude acoustic field sets the host fluid into motion. A scheme for the realization of such flow systems is outlined and a simple microflow system that implements this scheme is fabricated and tested.

Radiation resistance of sequencing chips for in situ life detection.

Life beyond Earth may be based on RNA or DNA if such life is related to life on Earth through shared ancestry due to meteoritic exchange, such as may be the case for Mars, or if delivery of similar building blocks to habitable environments has biased the evolution of life toward utilizing nucleic acids. In this case, in situ sequencing is a powerful approach to identify and characterize such life without the limitations or expense of returning samples to Earth, and can monitor forward contamination. A new semiconductor sequencing technology based on sensing hydrogen ions released during nucleotide incorporation can enable massively parallel sequencing in a small, robust, optics-free CMOS chip format. We demonstrate that these sequencing chips survive several analogues of space radiation at doses consistent with a 2-year Mars mission, including protons with solar particle event-distributed energy levels and 1 GeV oxygen and iron ions. We find no measurable impact of irradiation at 1 and 5 Gy doses on sequencing quality nor on low-level hardware characteristics. Further testing is required to study the impacts of soft errors as well as to characterize performance under neutron and gamma irradiation and at higher doses, which would be expected during operation in environments with significant trapped energetic particles such as during a mission to Europa. Our results support future efforts to use in situ sequencing to test theories of panspermia and/or whether life has a common chemical basis.

Development of the Ion Torrent CMOS chip for DNA sequencing

We describe a novel CMOS mixed signal sensor array chip that performs massively parallel DNA sequencing. This technology, in the form of a single-use, disposable chip, is the functional core of the Ion Torrent DNA sequencing platform. This is the first CMOS device capable of performing DNA sequencing, and the use of scalable CMOS chip architecture allows up to 1 billion simultaneous sequencing reactions to be performed on-chip. This enables the “

Surface micromachining for microelectromechanical systems

1000 Genome”, a long sought performance milestone for the rapidly emerging field of Genomic Personalized Medicine.