Vincent Malba

Monolithic high-performance three-dimensional coil inductors for wireless communication applications

An on-chip three-dimensional RF coil inductor is proposed as a key component to implement monolithic wireless transceivers. The device achieves a substantially superior performance compared to conventional spiral inductors, and is amenable to monolithic integration in a standard IC process due to its low thermal budget. Experimental devices fabricated on a standard silicon substrate (10 /spl Omega/-cm) achieve a 2.6 nH inductance with a peak quality-factor (Q) of 13 at 900 MHz. The Q-factor is limited by a lossy adhesive used in the fabrication. In a modified process without adhesive in the coil area, a 4.8 nH inductor achieves a peak Q-value of 30 at 1 GHz. High-Q 8 nH and 13.8 nH inductors have also been fabricated.

Laser-Lathe Lithography—a Novel Method for Manufacturing Nuclear Magnetic Resonance Microcoils

A novel 3-dimensional laser-lathe process for manufacturing magnetic resonance microcoils is presented. The process has been used to print coils on a variety of materials, including glass and Teflon. The dimensions of these coils can be varied easily to allow any number of different coil designs, including solenoids and saddle coils. In our fabrication process, capillary tubes sputter-coated with a thin titanium-copper multilayer are plated with a positive electrodeposited photoresist. The resist is exposed with a computer-controlled laser-lathe apparatus consisting of an argon-ion laser, an acousto-optic modulator, a movable aperture, a lead screw stage and a spindle stage. After exposure and development, copper is electrolytically deposited through the resist mask. Following copper deposition the resist mask is removed and the sputtered copper and titanium are etched away, leaving a microcoil firmly adhered to the capillary. The resistivity of the laser-lathe copper windings is 7.6% higher than the resistivity of hand-wound coils (1.85 μΩ-cm for laser-lathe copper compared with 1.72 μΩ-cm for bulk annealed copper). For laser-lathe and hand-wound microcoils of similar size and geometry, the coil quality factor, Q, of the laser patterned coils would be 7.6% lower than the hand-wound coils. Examples of 13C NMR spectra obtained using laser-lathe coils are shown, and a relative improvement of 68 in the NMR sensitivity is calculated for a laser-lathe microcoil compared with a conventional 5 mm NMR sample tube.

Steerable Catheter Microcoils for Interventional MRI: Reducing Resistive Heating

RATIONALE AND OBJECTIVES The aims of this study were to assess resistive heating of microwires used for remote catheter steering in interventional magnetic resonance imaging and to investigate the use of alumina to facilitate heat transfer to saline flowing in the catheter lumen. MATERIALS AND METHODS A microcoil was fabricated using a laser lathe onto polyimide-tipped or alumina-tipped endovascular catheters. In vitro testing was performed on a 1.5-T magnetic resonance system using a vessel phantom, body radiofrequency coil, and steady-state pulse sequence. Resistive heating was measured with water flowing over a polyimide-tip catheter or saline flowing through the lumen of an alumina-tip catheter. Preliminary in vivo testing in porcine common carotid arteries was conducted with normal blood flow or after arterial ligation when current was applied to an alumina-tip catheter for up to 5 minutes. RESULTS After application of up to 1 W of direct current power, clinically significant temperature increases were noted with the polyimide-tip catheter: 23°C/W at zero flow, 13°C/W at 0.28 cm(3)/s, and 7.9°C/W at 1 cm(3)/s. Using the alumina-tip catheter, the effluent temperature rise using the lowest flow rate (0.12 cm(3)/s) was 2.3°C/W. In vivo testing demonstrated no thermal injury to vessel walls at normal and zero arterial flow. CONCLUSIONS Resistive heating in current carrying wire pairs can be dissipated by saline coolant flowing within the lumen of a catheter tip composed of material that facilitates heat transfer.

High-performance RF coil inductors on silicon

Strong demand for wireless communication devices has motivated research directed toward monolithic integration of transceivers. The fundamental electronic component least compatible with silicon integrated circuits is the inductor, although a number of inductors are required to implement oscillators, filters and matching networks in cellular devices. Spiral inductors have been integrated into the silicon IC metallization sequence but have not performed adequately due to coupling to the silicon which results in parasitic capacitance and loss. We have, for the first time, fabricated three-dimensional coil inductors on silicon which have significantly lower capacitive coupling and loss and which now exceed the requirements of potential applications. Quality factors of 30 at 1 GHz have been measured in single turn devices and Q>16 in 2 and 4 turn devices. The reduced Q for multiturn devices appears to be related to eddy currents in outer turns generated by magnetic fields from current in neighboring turns. Higher Q values significantly in excess of 30 are anticipated using modified coil designs.

Endovascular Catheter for Magnetic Navigation under MR Imaging Guidance: Evaluation of Safety In Vivo at 1.5T

BACKGROUND AND PURPOSE: Endovascular navigation under MR imaging guidance can be facilitated by a catheter with steerable microcoils on the tip. Not only do microcoils create visible artifacts allowing catheter tracking, but also they create a small magnetic moment permitting remote-controlled catheter tip deflection. A side product of catheter tip electrical currents, however, is the heat that might damage blood vessels. We sought to determine the upper boundary of electrical currents safely usable at 1.5T in a coil-tipped microcatheter system. MATERIALS AND METHODS: Alumina tubes with solenoid copper coils were attached to neurovascular microcatheters with heat shrink-wrap. Catheters were tested in carotid arteries of 8 pigs. The catheters were advanced under x-ray fluoroscopy and MR imaging. Currents from 0 mA to 700 mA were applied to test heating and potential vascular damage. Postmortem histologic analysis was the primary endpoint. RESULTS: Several heat-mitigation strategies demonstrated negligible vascular damage compared with control arteries. Coil currents ≤300 mA resulted in no damage (0/58 samples) compared with 9 (25%) of 36 samples for > 300-mA activations (P = .0001). Tip coil activation ≤1 minute and a proximal carotid guide catheter saline drip > 2 mL/minute also had a nonsignificantly lower likelihood of vascular damage. For catheter tip coil activations ≤300 mA for ≤1 minute in normal carotid flow, 0 of 43 samples had tissue damage. CONCLUSIONS: Activations of copper coils at the tip of microcatheters at low currents in 1.5T MR scanners can be achieved without significant damage to blood vessel walls in a controlled experimental setting. Further optimization of catheter design and procedure protocols is necessary for safe remote control magnetic catheter guidance.

Integration of vapor deposited polyimide into a multichip module packaging process

We report the first full integration of a vapor-deposited polyimide dielectric into a multichip module (MCM) electronic packaging scheme. A robust high-throughput vapor deposition polymerization (VDP) of polyimide has been developed for an interconnection scheme in which thin film metal interconnects are patterned from the top of bare die, down the sides, and onto the substrate circuit board surface. VDP polyimides films have been extensively characterized using infrared spectroscopy and prism coupling techniques. The chemical and electrical properties of the VDP polyimide films are similar to commercially available spin cast polyimides.

Vapor deposition polymerization of polyimide for microelectronic applications

We report the high-throughput vapor deposition polymerization (VDP) of smooth, uniform polyimide films for microelectronic applications. Using infrared (IR) spectroscopy, waveguiding refractive index measurements, atomic force microscopy, and matrix assisted laser desorption ionization, we have characterized both cured and uncured films. Uncured VDP films consist of oligomers (up to tetramers) and unreacted monomeric species. Cured VDP films are chemically identical to commercially available spin cast polyimides. Both IR and refractive index anisotropy are used to determine the extent of cure, and the stoichiometry of the cured film. Integration of the VDP films into a multichip module process is presented, and the application of VDP films in ultra-large-scale integrated circuit manufacturing is discussed. Finally, the vapor deposition of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine, a high performance polyimide system, is presented.

Laser surface modification for selective electroplating of metal: A 2.5 m/s laser direct write process

A very fast laser direct write process is described. The process involves laser modification of an insulating seed multilayer to form a conducting surface which can be electroplated. The seed layer is composed of an adhesion layer of TiW, a conducting layer of Au, and a top insulating layer of α‐Si. The laser forms a Au‐Si mixture without substantially affecting the adhesion layer. Writing speeds of 2.5 m/s have been demonstrated. The laser patterning can be performed in air, and the process works over a broad range of laser power (Pmax/Pmin ∼ 5).

Magnetically-Assisted Remote Controlled Microcatheter Tip Deflection under Magnetic Resonance Imaging.

X-ray fluoroscopy-guided endovascular procedures have several significant limitations, including difficult catheter navigation and use of ionizing radiation, which can potentially be overcome using a magnetically steerable catheter under MR guidance. The main goal of this work is to develop a microcatheter whose tip can be remotely controlled using the magnetic field of the MR scanner. This protocol aims to describe the procedures for applying current to the microcoil-tipped microcatheter to produce consistent and controllable deflections. A microcoil was fabricated using laser lathe lithography onto a polyimide-tipped endovascular catheter. In vitro testing was performed in a waterbath and vessel phantom under the guidance of a 1.5-T MR system using steady-state free precession (SSFP) sequencing. Various amounts of current were applied to the coils of the microcatheter to produce measureable tip deflections and navigate in vascular phantoms. The development of this device provides a platform for future testing and opportunity to revolutionize the endovascular interventional MRI environment.

Vapor deposition of polyimide: segregation of partially reacted species at the polyimide/Si (100) interface

Abstract We examined the vapor deposition of polyimide produced by co-evaporation of pyromellitic dianhydride and oxydianiline. Using internal reflectance spectroscopy and prism coupling techniques, we monitored the effects of varying relative monomer fluxes on cured film stoichiometry. We observed the effects of monomer interdiffusion during the ex-situ curing leading to segregation of partially reacted species at the film/substrate interface. Such interface segregation may be influential in determining adhesion of polyimide to metal layers for microelectronics applications.