Steve Wakeham

Stability of thin film transistors incorporating a zinc oxide or indium zinc oxide channel deposited by a high rate sputtering process

A novel rf sputtering technology in which a high density plasma is created in a remote chamber has been used to reactively deposit zinc oxide (ZnO) and indium zinc oxide (IZO) thin films at room temperature from metallic sputtering targets at deposition rates ∼50 nm min −1 , which is approximately an order of magnitude greater than that of rf magnetron sputtering. Thin film transistors have been fabricated using IZO with a maximum processing temperature of 120 ◦ C, which is defined by the curing of the photoresist used in patterning. Devices have a saturated field effect mobility of 10 cm 2 V −1 s −1 and a switching ratio in excess of 10 6 . Gate bias stress experiments performed at elevated temperatures show a consistent apparent increase in the field effect mobility with time, which is attributed to a charge trapping phenomenon.

High-k (k=30) amorphous hafnium oxide films from high rate room temperature deposition

Amorphous hafnium oxide (HfOx) is deposited by sputtering while achieving a very high k∼30. Structural characterization suggests that the high k is a consequence of a previously unreported cubiclike short range order in the amorphous HfOx (cubic k∼30). The films also possess a high electrical resistivity of 1014 Ω cm, a breakdown strength of 3 MV cm−1, and an optical gap of 6.0 eV. Deposition at room temperature and a high deposition rate (∼25 nm min−1) makes these high-k amorphous HfOx films highly advantageous for plastic electronics and high throughput manufacturing.

The impact of substrate bias on a remote plasma sputter coating process for conformal coverage of trenches and 3D structures

With the progression towards higher aspect ratios and finer topographical dimensions in many micro- and nano-systems, it is of technological importance to be able to conformally deposit thin films onto such structures. Sputtering techniques have been developed to provide such conformal coverage through a combination of coating re-sputtering and ionised physical vapour deposition (IPVD), the latter by use of a secondary plasma source or a pulsed high target power (HiPIMS). This paper reports on the use of an alternate remote plasma sputtering technique in which a high density (>1013 cm−3) magnetised plasma is used for sputter deposition, and additionally is shown to provide IPVD and a re-sputtering capability. From the substrate I–V characteristics and optical emission spectroscopy (OES) data, it is shown that remote plasma sputtering is an inherently continuous IPVD process (without the need of a secondary discharge). Through the reactive deposition of Al2O3 onto complex structures, scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) results demonstrate that applying a negative substrate bias during film growth can result in re-sputtering of deposited material and film growth on surfaces obscured from the initial sputter flux. Using 5 : 1 (height : width) aspect ratio trenches, the substrate bias was set to 0,−245 and −334 V. At 0 V substrate bias, the alumina coating is predominantly deposited on the horizontal surfaces; at −344 V, it is predominantly deposited onto the side walls and at −245 V a more uniform layer thickness is obtained over the trench. The process was optimised further by alternating the substrate bias between −222 and −267 V, with a 50% residence time at each voltage, yielding a more uniform conformal coverage of the 5 : 1 aspect ratio structures over large areas.

Laser annealing of thin film electroluminescent devices deposited at a high rate using high target utilization sputtering

This paper presents the photoluminescent (PL) and electroluminescent (EL) characteristics of ZnS:Mn deposited at room temperature using high target utilization sputtering (HiTUS). Significant improvements in PL intensity are seen when ZnS:Mn is deposited using HiTUS instead of conventional RF magnetron sputtering. When incorporated as part of a complete EL device with yttrium oxide forming the dielectric layers and indium tin oxide used as the top contact electrode, localized laser annealing of the ZnS:Mn phosphor layer is shown to provide enhancement of the EL characteristics.

Transparent and Flexible Thin Film Electroluminescent Devices Using HiTUS Deposition and Laser Processing Fabrication

Highly transparent thin film electroluminescent structures offering excellent switch on characteristics, high luminance and large break-down voltages have been deposited onto glass and flexible polymeric materials with no substrate heating using high target utilization sputtering. Deposition of ZnS:Mn as the active light emitting layer and Y₂O₃, Al₂O₃, Ta₂O₅, and HfO₂ as dielectric materials arranged in single and multiple layer configurations were investigated. Devices incorporating Al₂O₃, HfO₂ quadruple layers demonstrate the highest attainable luminance at low threshold voltage. Single pulse excimer laser irradiation of the phosphor layer prior to deposition of the top dielectric layer enhanced the luminance of the devices. The devices fabricated on glass and polymeric substrates exhibited a maximum luminance of 500 and 450 cdm^-2 when driven at 270 VRMS and 220 VRMS, respectively, with a 1.0 kHz sine wave.

Laser damage threshold results for sputtered coatings produced using different deposition technologies

A new sputter deposition process has been developed based upon remote generation of plasma by a dedicated Plasma Source (PLS). This technique is referred to as high target utilisation sputtering (HiTUS). In contrast to ion beam and magnetron sputtering processes, HiTUS allows fast deposition rates of low stress, high density films from a high percentage (>90%) of the target surface. The process has not previously been applied to thin films for high laser damage threshold applications. The paper will present results of the anti-reflection (AR) coating trials and compare them to two other coating deposition processes - standard e-beam evaporation and hollow cathode ion-assisted e-beam deposition.