An all-dry silicon-etch based micromachining process for neural probes was demonstrated in the manufacture of a probe with a 32-site recording electrode array. The fork-like probe shafts were formed by double-sided deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) substrate, with the buried SiO 2 layer acting as an etch stop. The shafts typically had the dimensions 5 mm × 25 µm × 20 µm and ended in chisel-shaped tips with lateral taper angles of 4 •. An array of Ir electrodes, each 100 µm 2 , and Au conductor traces were formed on top of the shafts by e-beam evaporation. An accompanying interconnect solution based on flexible printed circuitry was designed, enabling precise and flexible positioning of the probes in neural tissue. SEM studies showed sharply defined probes and probe tips. The electrical yield and function were verified in bench-top measurements in saline. The magnitude of the electrode impedance was in the 1 M range at 1 kHz, which is consistent with neurophysiological recordings.

Interfacial reactions and thermal stability of ultrahigh vacuum deposited multilayered Mo/Si structures

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Thermally stable amorphous ( Al Mo Nb Si Ta Ti V Zr ) 50 N 50 nitride film as diffusion barrier in copper metallization Appl. Phys. Lett. 92, 052109 (2008); 10.1063/1.2841810 Thermal stability of the interfaces between Co-, Ni-, and Fe-based ferromagnets in contact with selected nitrides M N ( M = Al , B, Nb, Ta, Ti, and V) J. Appl. Phys. 98, 053907 (2005); 10.1063/1.2040002 An evidence of trap activation for positive temperature coefficient of resistivity in BaTiO 3 ceramics with substitutional Nb and Mn as impuritiesWe present measurements of the pseudobinary phase diagram of the TiSi 2 -NbSi 2 system. This disilicide system has recently become important because of the enhanced formation of the low resistivity C54 phase of TiSi 2 by addition of Nb. The solubility limit of Nb in C54 TiSi 2 at 1000°C is found to lie between 10% and 16% at the metal site, and the solubility limit of Ti in C40 NbSi 2 at 1000°C is between 76% and 79.5% at the metal site. Adding Nb to C54 TiSi 2 increases the unit cell volume at a rate of 0.035% per at. % Nb. Adding Nb to C40 ͑Ti,Nb͒Si 2 increases the unit cell volume at a rate of 0.034% per at. % Nb. The presence of Nb enhances the formation of the C54 phase and improves its thermal stability. The desirable low resistivity of the C54 phase is increased by 1.2 ⍀ cm per at. % Nb.

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The influence of interfacial Mo on the formation of TiSi2 is studied using 120 nm Ti layers deposited on Si (100) substrates. After annealing at 450 °C, C54 TiSi2 and C40 (Ti,Mo)Si2 are found in the samples initially having an interposed layer of Mo 1.6–2 nm thick. In the absence of Mo, only C49 TiSi2 is obtained. The pathway for the formation of C54 TiSi2 is altered from the usual C49–C54 phase transformation to the epitaxial growth of C54 TiSi2 on C40 (Ti,Mo)Si2. The resistivity of the TiSi2 layers formed is about 14 and 61 μΩ cm for the C54 and C49 phase, respectively. However, for equal annealing time, the thickness of the C49 TiSi2 formed is about ten times that of the C54 TiSi2 grown on C40 (Ti,Mo)Si2, because of the barrier effects on Mo or C40 (Ti,Mo)Si2 on Si diffusion. The experimental results are discussed on the basis of energetic arguments to account for the suppressed formation of C49 TiSi2 and the enhanced formation of C54 TiSi2 at 450 °C.

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