Use of Microhotplate Arrays as Microdeposition Substrates for Materials Exploration

Abstract

An approach for high-throughput rapid screening of chemical vapor deposition (CVD) materials using micromachined silicon microheater arrays is described. To illustrate this approach, titanium dioxide was deposited by CVD, using titanium(IV) nitrate and titanium-(IV) isopropoxide at temperatures between 130 and 815 °C. Deposition was confined to the microhotplate elements within 4-and 16-element arrays. Film microstructure was examined by scanning electron microscopy. In situ electrical measurements were made with integrated microcontacts during the deposition of TiO 2 using titanium(IV) isopropoxide. A novel approach using temperature-programmed deposition with temperature ramp rates up to 800 °C/s was also employed for microstructure modification during deposition. Additionally, the steep temperature gradients present on the microhotplate supports have been demonstrated to provide an excellent platform for investigating temperature-dependent microstructures.

Measurement of minority-carrier diffusion lengths using wedge-shaped semiconductor photoelectrodes

“…Tungsten trioxide, WO 3 , and bismuth vanadate, BiVO 4 , were chosen as proof-of-concept materials to demonstrate the technique on candidate photoanodes for use in a PEC device.…”

“…A detailed analysis was performed to realize and verify a conformal and insulating ALD-treatment of the pores and to obtain a uniform polishing of the top surface (see ESI †). Electrochemical measurements were performed in a custom electrochemical cell that was equipped with a xed-position working electrode, a Pt mesh counter electrode, and a Ag/AgCl 4 . Control experiments veried that the stirring and/or electrode placement did not affect the measured data, due to the small currents involved and the high concentration of the electrolyte.…”

“…A 455 nm LED and a 500 nm LED that produced an optical output power similar to that of the 365 nm LED were also used as the illumination sources for data collection from the Si wedge sample. A Newport 150 W Xe arc lamp coupled to a Cornerstone 1/4 m monochromator was used for spectrally varied photocurrent measurements of BiVO 4 .…”

“…Automated methods of producing new semiconducting materials [2][3][4][5] have resulted in a growing number of materials that appear to be promising candidates for use in PEC systems. 6 Properties such as the band gap and carrier lifetimes 7,8 can be screened rapidly, but a critical property for the realization of a high performance PEC cell, the minority-carrier diffusion length, L, requires detailed measurement techniques and protocols.…”

Full-wafer mapping and response surface modeling techniques for thin film deposition processes

“…Hyett and Parkin [7] describe a crossflow reactor configuration where separate precursor inlet nozzles are used to produce films with composition gradients of tungsten and titanium oxides and to likewise generate films with varying ratios of TiO 2 rutile/anatase phases. In Taylor and Semancik [12], microhotplate devices were used to control the temperature in an array of micro-scale substrate samples; it was found that temperature gradients in the microhotplate supports resulted in a microstructurally graded film on the support legs. Finally, the Programmable Reactor system [5,6,9,10] features a segmented shower head design where each segment is fed individually with reactant gases and exhaust gas is pumped back up through each segment.…”