Past Research

IDT Sensors

Novel, high capacitance interdigital structures based on branched carbon nanotubes (B-CNTs) are realized using plasma enhanced chemical vapor deposition. Extensive overlapping between parallel fingers due to the branched carbon nanostructures leads to high capacitance values in the fabricated interdigital structures. A significant rise in the capacitance up to 100 times is reported by means of branched carbon nanotubes. The high electron emission of such nanostructures over regular CNTs can be applied to realize high sensitivity sensors. To investigate the functionality of fabricated B-CNT-based actuator, both sensor and actuator configurations have been designed on a silicon-based membrane and the electromechanical response of the whole structure has been investigated. These structures show a superior actuation behavior owing to their high capacitance due to extensive overlapping fingers.

ISFET

We report the realization of high-sensitivity ionselective field-effect transistors (ISFETs) using nanoporous polysilicon on the gate region. Owing to the presence of a nanoporous film, the effective area of the exposed surface becomes larger than that of the channel area of a regular transistor. The response of such transistors to pH has been measured for a wide range from four to nine, showing a different behavior from regular ISFETs where a change in the threshold voltage is recorded. A relative current-based sensitivity can be adapted for such devices. A high sensitivity on the order of 300 mV/pH is reported, owing to the presence of 3-D nanostructures.

Carbon Nanotubes

We report the application of vertically grown carbon nanotubes  (CNTs)  for submicron and nanolithography. The growth of CNTs is performed on silicon substrates using a nickel-seeded plasma-enhanced chemical vapor deposition method at a temperature of 650 °C and with a mixture of C2H2 and H2. The grown CNTs are encapsulated by a titanium-dioxide film and then mechanically polished to expose the buried nanotubes, and a plasma ashing step finalizes the process. The emission of electrons from the encapsulated nanotubes is used to write patterns on a resist-coated substrate placed opposite to the main CNT holding one. Scanning electron microscope has been used to investigate the nanotubes and the formation of nano-metric lines. Also a novel approach is presented to create isolated nanotubes from a previously patterned cluster growth.

Plastic Micromachining

Etching of poly-ethylene terephathalate (PET) is achieved using a chemical solution in di-methyl-formamide assisted by ultra-violet illumination. Deep vertical features suitable for plastic micro-machining, are obtained with features of the order of 2 lm and aspect ratios of the order of 10. By using tin (Sn) as the masking layer, the problem of crack formation on the PET surface during this photochemical etching technique is totally resolved. High etch-rates as 20 um/h are obtained at a low etching temperature of 60 C. To improve the thermal dissipation during the etching and to minimize the plastic shrinkage, a layer of silicone–rubber is applied on the backside of the PET. We have successfully fabricated and assembled an all-plastic one directional micro-valve. Preliminary plastic-based micro-structures are demonstrated.

Gas Sensors

Ultrahigh-sensitivity SnO2-CuO sensors were fabricated on Si (100) substrates for detection of low concentrations of hydrogen sulfide. The sensing material was spin coated over platinum electrodes with a thickness of 300 nm applying a sol-gel process. The SnO2-based sensors doped with copper oxide were prepared by adding various amounts of Cu(NO3)2 3H2O to a sol suspension. Conductivity measurements of the sensors annealed at different temperatures have been carried out in dry air and in the presence of 100 ppb to 10-ppm H2S. The nanocrystalline SnO2-CuO thin films showed excellent sensing characteristics upon exposure to low concentrations of H2S below 1 ppm. The 5% CuO-doped sensor having an average grain size of 20 nm exhibits a high sensitivity of 2.15 106 (Ra Rg) for 10-ppm H2S at a temperature of 85 C. By raising the operating temperature to 170 C, a high sensitivity of 105 is measured and response and recovery times drop to less than 2 min and 15 s, respectively. Selectivity of the sensing material was studied toward various concentrations of CO, CH4, H2, and ethanol. SEM, XRD, and TEM analyses were used to investigate surface morphology and crystallinity of SnO2 films.

You are here:

Thin Film Laboratories,

Electric & Computer Engineering Department,

Faculty of Engineering, Campus #2
University of Tehran
Kargar Shomali St. (Passed the Jalal-Al-Ahmad St.,
Across the Ninth Lane)
Tehran, Iran

Tel : +98 21 8020403   Ext.3545