Suwen Li

A 200-Channel Area-Power-Efficient Chemical and Electrical Dual-Mode Acquisition IC for the Study of Neurodegenerative Diseases

Microelectrode array (MEA) can be used in the study of neurodegenerative diseases by monitoring the chemical neurotransmitter release and the electrical potential simultaneously at the cellular level. Currently, the MEA technology is migrating to more electrodes and higher electrode density, which raises power and area constraints on the design of acquisition IC. In this paper, we report the design of a 200-channel dual-mode acquisition IC with highly efficient usage of power and area. Under the constraints of target noise and fast settling, the current channel design saves power by including a novel current buffer biased in discrete time (DT) before the TIA (transimpedance amplifier). The 200 channels are sampled at 20 kS/s and quantized by column-wise SAR ADCs. The prototype IC was fabricated in a 0.18 μm CMOS process. Silicon measurements show the current channel has 21.6 pArms noise with cyclic voltammetry (CV) and 0.48 pArms noise with constant amperometry (CA) while consuming 12.1 μW. The voltage channel has 4.07 μVrms noise in the bandwidth of 100 kHz and 0.2% nonlinearity while consuming 9.1 μW. Each channel occupies 0.03 mm2 area, which is among the smallest.

Carbon Nanotube Contact Plug on Silicide for CMOS Compatible Interconnect

Carbon nanotube (CNT) filled contact plugs with silicide as the bottom electrode have been demonstrated in this letter. Nickel has been used as the main catalyst to achieve CMOS compatibility. By modifying the catalyst from a pure Ni single layer structure to a Ni/Al/Ni multilayer composite, uniform selective CNT growth on Ti silicide substrate has been achieved. At a low temperature of 450 °C, the vertically aligned CNTs with a density of 1.1×1011 tubes/cm2 inside the silicon dioxide contact plug are formed without the need of catalyst patterning. Four-point Kelvin structures are designed to measure the resistance of the CNT filled contact plugs. Measurement results show that an ohmic contact plug resistance of 216 Ω·μm2 is obtained.

Contact resistance reduction of carbon nanotube via through O2 plasma post-synthesis treatment

The cause of high contact resistance between carbon nanotube (CNT) filled vias and metal electrodes is studied. Contamination due to the chemical–mechanical polishing (CMP) process, which damages the sp2 bonds at the end of the CNTs, is found to be the main cause. An alternative oxygen plasma etching process is proposed to preserve the sp2 bonds at the CNT tips during the via planarization process. The improved properties of the CNT tips, with more sp2 bonds and fewer oxygen-containing groups, have been demonstrated using X-ray photoelectron spectroscopy (XPS). Based on the findings, a new CNT via integration process is designed, which includes selective CNT growth inside the via and O2 plasma planarization. A low contact resistance of 1.83 μΩ cm2 is demonstrated.

Ultralow-

An interlayer dielectric with an extremely low dielectric constant of 1.96 is demonstrated using SiO2 with vertically aligned cylindrical pores. Vertically grown carbon nanotubes are used as a template for the cylindrical pores to achieve high porosity while maintaining structural stability. Measurements show that an elastic modulus of 17.5 GPa can be maintained even at 65% porosity to provide sufficient mechanical strength for most back end of line processes. This represents a 94% improvement in mechanical stability compared with the state-of-the-art low-k dielectrics. The tradeoffs between dielectric constant and elastic modulus of different porous structures have also been studied to project the ultimate achievable k-value.

k

Dopamine is a neurotransmitter that plays a key role in neural disorders. This paper reports on the design and fabrication of a microelectrode array (MEA) modified with multi-walled carbon nanotubes (MWCNTs) to detect dopamine with high sensitivity. The modification is based on covalent bonding of carboxylic groups in carbon nanotubes (CNTs) and amine groups in poly-l-lysin (PLL). The modified microelectrode array was characterized by Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The CNT-coated MEA shows a sensitivity of 1186 nA/μM·mm2·(V/s)0.5 in dopamine detection. This enhanced sensitivity suggests that CNT-coated MEA is a promising platform for in vitro high-throughput, high sensitivity neurotransmitter detection.

Dielectric With Nanotubes Assisted Vertically Aligned Cylindrical Pores

The contact property between Ge2Sb2Te5 (GST) with vertical carbon nanotubes (CNTs) is studied in this work. By careful catalyst design and process optimization, we have demonstrated the formation of ohmic contact between the CNT and the GST material. The developed process is CMOS compatible and can be used for form phase change memory over the vias in the interconnect layers.

Multi-walled carbon nanotube coated microelectrode array for high-throughput, sensitive dopamine detection

Phase change memory (PCM) formed by Ge2Sb2Te5 (GST) on vertical carbon nanotube (CNT) filled contact plug is demonstrated in this paper. In order to achieve compatibility with the underlying process, the CNTs are synthesized using nickel catalyst at a low temperature. Reasonable contact characteristics between the CNTs and GST are achieved without material compatibility problem. Due to the small contact size of the CNT to the phase change material, a significant reduction in programming power is achieved compared to metal contact at the same via size. The temperature simulation result shows that the CNT filled via helps to reduce the programing area. The fabricated PCM on CNT filled via is able to endure more than 104 SET/RESET cycles without observable degradation.

Ohmic contact formation between Ge 2 Sb 2 Te 5 phase change material and vertically aligned carbon nanotubes

This paper describes the potential of using carbon nanotube (CNT) as a via-filling material to enhance the performance mainstream CMOS technology. Due to the CMOS compatibility constraint, the choice of catalyst material and processing conditions have been significantly limited. After a careful selection process, Ni is found to be a workable material. Through catalyst engineering, we have demonstrated that it is possible to form CNT filled vias on metal or silicide substrate at low temperature with low contact resistance. The impact of via dimensions and processing condition has also been studied. Based on statistical analysis using measured data, the best-case projected via resistance for a 30nm via is 295Ω, which is within one order of magnitude of its copper and tungsten counterparts.

Low Power Phase Change Memory With Vertical Carbon Nanotube Electrode

The application of carbon-nanotube to reduce interconnect delay is studied in this work, with the emphasis on how it can be used to reduce the inter-metal capacitance. By forming vertically aligned cylindrical pores assisted by vertically grown CNT, mechanically stable ultra-low-k interlayer dielectric with k-value down to 1.89 is experimentally demonstrated. Ways to integrate this process will other CNT enhanced interconnect technology are also discussed.