Wednesday, November 29, 2017

Transparent flexible capacitors by ALD high-k, ALD AZO and graphene electrodes

Transparent and flexible flat panel displays manufactured on plastic substrates and flexible substrates involve key technologies like ALD manufacturing of transparent electrodes and barriers. In addition, for the pixel-drive circuit of displays, capacitors are used for charging and discharging at very high speed. Having a high capacitance enables also a high color brightness for each pixel. Now researchers at Wuhan University, China has developed an capacitor technology that is has an excellent transparency and flexibility using the latest ALD and graphene processing technology. Please find the Open Access publication below.

In this study used comercially available graphene in the form of single-layer graphene that had been grown by CVD on copper foil from 2D Carbon Tech Inc. LTD, Changzhou, China. The ALD ZrO2 high-k and AZO was grown in an TSF 200 from Beneq.

Transparent and Flexible Capacitors with an Ultrathin Structure by Using Graphene as Bottom Electrodes
by Tao Guo, Guozhen Zhang, Xi Su, Heng Zhang, Jiaxian Wan, Xue Chen, Hao Wu and Chang Liu
Nanomaterials 2017, 7(12), 418; doi:10.3390/nano7120418  (registering DOI) - 28 November 2017
(Left) The schematic diagram of the ultrathin, transparent and flexible capacitors; (Right) The optical transmittance spectra of the capacitors on PEN substrates. The inset shows the optical photograph of the actual capacitor device with the characters “TFS 200” in the background, and the optical transmittance spectra of graphene and capacitors on quartz substrates. 
Ultrathin, transparent and flexible capacitors using graphene as the bottom electrodes were directly fabricated on polyethylene naphthalate (PEN) substrates. ZrO2 dielectric films were deposited on the treated surface of graphene by atomic layer deposition (ALD). The deposition process did not introduce any detectible defects in the graphene, as indicated by Raman measurements, guaranteeing the electrical performances of the graphene electrodes. The Aluminum-doped zinc oxide (AZO) films were prepared as the top electrodes using the ALD technique. The capacitors presented a high capacitance density (10.3 fF/μm2 at 10 kHz) and a relatively low leakage current (5.3 × 10−6 A/cm2 at 1 V). Bending tests revealed that the capacitors were able to work normally at an outward bending radius of 10 mm without any deterioration of electrical properties. The capacitors exhibited an average optical transmittance of close to 70% at visible wavelengths. Thus, it opens the door to practical applications in transparent integrated circuits. Full article

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).