Bruce C. Kim

Polyimide-based intracortical neural implant with improved structural stiffness

A novel structure for chronically implantable cortical electrodes using polyimide bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and the skull and at the brain/implant interface and stiffness for better surgical handling. A 5–10 µm thick silicon backbone layer was attached to the tip of the electrode to enhance the structural stiffness. This stiff segment was then followed by a 1 mm flexible segment without a silicon backbone layer. The fabricated implants have tri-shanks with five recording sites (20 µm × 20 µm) and two vias of 40 µm × 40 µm on each shank. In vitro cytotoxicity tests of prototype implants revealed no adverse toxic effects on cells. Bench test impedance values were assessed, resulting in an average impedance value of ~2 MΩ at 1 KHz. For a 5 µm thick silicon backbone electrode, the stiffness of polyimide-based electrodes was increased ten times over that of electrodes without the silicon backbone layer. Furthermore, polyimide-based electrodes with 5 µm and 10 µm thick silicon backbone layer penetrated pia of rat brain without buckling that has been observed in implants without silicon reinforcement.

An approach for selection of test points for analog fault diagnosis

This paper presents an algorithm for the selection of test points in frequency domain analysis of analog circuits. The proposed algorithm aims to find an optimum number of test points to isolate faults based on minimization of ambiguity groups using an information measure. This technique can be used for identifying catastrophic faults. The algorithm is composed of two stages. In the first stage, a fault dictionary is created and in the second stage, the required test points are selected based on the information measure provided by the test points. Two example circuits are presented to demonstrate the effectiveness of the proposed algorithm.

MEMS spring probe for non-destructive wafer level chip test

MEMS spring probes were fabricated for non-destructive testing of ultra-small pad-pitch chips. The probes had high suspension from the bottom planar surface, uniformity, high elastic spring constant and low contact resistivity. All contacts took place simultaneously. The contact area at the tip was 70 µm2. Fabricated probes showed great spring properties when compression force was applied from the top glass substrate. No noticeable physical markings were observed on the pads over a known range of compression. At the contact resistivity test, as the compression force was increased, the contact resistivity was decreased due to increase of contact surface area. Low RF signal loss was observed through metal probes due to low resistive loss and capacitive parasitics. Measured scattering parameter S11 was approximately −50 dB and S21 was −0.5 dB up to 30 GHz. Inductance and capacitance of the MEMS probe were negligible.

A new design for built-in self-test of 5GHz low noise amplifiers

This paper presents a new low-cost built-in self-test (BIST) circuit for 5GHz low noise amplifier (LNA). The BIST circuit is designed for system-on-chip (SOC) transceiver environment. The proposed BIST circuit measures the LNA specifications such as input impedance, voltage gain, noise figure, and input return loss all in a single SoC environment.

Benzocyclobutene (BCB) based intracortical neural implant

A novel structure for chronically implantable cortical electrodes using new Benzocyclobutene (BCB) bio-polymer was devised, which provides both flexibility for micro-motion compliance between brain tissues and skull and stiffness for better surgical handling. BCB is very attractive polymer for stable long-term implant function, because it has flexibility, biocompatibility, low moisture uptake (<0.2 wt%), and low dielectric constant (/spl sim/2.6). For easy operation during surgical insertion, a 5/spl sim/10/spl mu/m thick silicon backbone layer is attached to the desired region of the electrode to increase the stiffness. It is then followed by 1 mm of flexible part of the electrode without silicon backbone layer designed to absorb stress from any micro-motion between the brain tissue and the electrode. The fabricated implants have tri-shanks with 5 recording sites (20x20/spl mu/m) and 2 vias (40x40/spl mu/m) on each shank. BCB electrodes with 5/spl mu/m and 10/spl mu/m thick backbone silicon penetrated pia of rat brain without buckling.

A new BIST scheme for 5GHz low noise amplifiers

This paper presents a new low-cost Built-In Self-Test (BIST) circuit for measuring gain, noise figure and input impedance of 5GHz low noise amplifier (LNA). The BIST circuit is designed using 0.18 µm SiGe technology. The test technique utilizes input impedance matching and output transient voltage measurements. The technique is simple and inexpensive.

Modeling and simulation of the thin film bulk acoustic resonator

This paper describes the modeling and simulation results for thin film BAW resonators. We present the frequency tuning mechanisms, the influence of the thickness of the electrodes and Q of the resonator. The BAW resonator was fabricated with the piezoelectric thin film and Bragg reflector.

A new test method for embedded passives in high density package substrates

This paper presents a new test technique for embedded passives in Multi-Chip Module (MCM) substrates. The technique uses an active circuit to test passive circuits in MCM substrates. The defect can be found with very high sensitivity due to the natural amplification of the op amp circuit used as a test apparatus. The technique is low-cost and can be applied to many different classes of passive filters that are embedded in MCM substrates.

Equivalent circuit design of multilayer parallel-coupled line filter

LTCC filters have been widely used for wireless LAN terminals. They generally adopt the multilayer structure. Some multilayer LTCC filters are made of symmetrical parallel-coupled lines and anti-symmetrical parallel-coupled lines to reduce the length of resonators. The equivalent circuit of parallel-coupled lines was analyzed and applied to bandpass filters using multilayer parallel-coupled line resonators. A three-pole bandpass filter with a center frequency of 2.45 GHz is designed by using the proposed equivalent circuit and the measured results have good agreement with the design results.

Fabrication of implantable polyimide based neural implants with flexible regions to accommodate micromovement

A unique structure for chronically implantable cortical electrodes using polyimide polymer was devised, which provides both flexibility between brain tissues and skull and stiffness for easy insertion. The fabricated implants are tri-shanks with 5 recording sites (20/spl times/20 /spl mu/m) and 2 vias per electrode of 40/spl times/40 /spl mu/m. Each recording site was connected to the external circuitry via a 15-channel connector, which is especially designed to facilitate processing of neural signals to the external circuitry. Measured impedance values are in /spl sim/2 Mohm at 1 KHz. For a 5 /spl mu/m thick silicon backbone electrode, the stiffness was improved 10 times larger than that of the electrode without silicon backbone layer. Stiff electrodes with 5 /spl mu/m and 10 /spl mu/m thick backbone silicon penetrated pia of rat without buckling.