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C-mems for The Manufacture of 3d Micro Batteries

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C-MEMS allows a wide assortment of fascinating new MEMS applications that utilize structures having a wide assortment of shapes, resistivity, and mechanical properties. In the current case, we utilized this method to yield high angle proportion carbon cathodes for micro-batteries. The upsides of utilizing photoresists as the beginning material for carbon anodes incorporate the way that photoresists can be designed by photolithography systems bringing about substantially better highlights than conceivable with the more customary silk screening of carbon inks and, in light of the fact that photoresists are extremely controlled and reproducible materials, more reproducible carbon cathode conduct can be normal.

Li-ion batteries use highly ordered Graphite as well as both soft and hard Carbons. Li batteries are for the most part dependent on the execution of bigger cells with limits of up to a few ampere-hours. With compact microbatteries, the packaging and internal battery components largely determine the overall size and weight of the assembled battery for implementation in miniature handheld electronic devices. Hence the power and energy densities that can be obtained do not scale favorably.

One approach to overcome the size and energy density deficiencies of 2D microbatteries is to develop 3D battery architectures based on specially designed arrays composed of high aspect ratio 3D electrode elements. The expected capacity of 3D batteries maybe 3.5 times higher than that of a 2D battery. The key challenge in fabricating 3D micro-batteries based on carbon-negative electrodes is in achieving a high aspect ratio (10:1) electrodes so that the areal footprint of a 3D battery can be less than 1 cm2 without compromising capacity. This paper provides the first report of the fabrication and lithium intercalation properties of high aspect ratio 3D carbon electrode arrays.


A schematic drawing of the C-MEMS fabrication process and typical scanning electron microscopy (SEM) photos of photoresist and carbon structures are shown in Figure.

The substrates used are (1) Si, (2) Si3N4 (2000 Å)/Si, (3) SiO2 (5000 Å)/Si, and (4) Au (3000 Å)/Ti (200 Å)/SiO2 (5000 Å)/Si.

Electron beam evaporation methods were used to deposit Ti, Au layers. A negative photoresist with different thicknesses, NANO SU-8 100, was spin-coated on substrates. To generate SU-8 posts, two types of mask designs were used:

  1. 180 3 180 arrays of circles with a diameter of 50, 40, 30, and 20 mm and center to center spacing of 100 mm
  2. 90 3 90 arrays of circles with a diameter of 100 mm and a 200 mm center to center spacing.

In a two-step pyrolysis system in an open-ended quartz-tube furnace, Photoresist based C-MEMS architectures were obtained in which samples were first post-baked in an atmosphere of N2 at 300 ° C for about 40 minutes first, then heated in an atmosphere of N2 at a flow rate of 2000 standard cubic centimeter per minute up to 900 ° C. Then the atmosphere was changed to form gas H2 (5 percent)/N2 that flowed at about 2000 sccm.

The sample was kept at 900°C for 1 h, then the heater was turned off and the samples were cooled in an N2 atmosphere to room temperature. The heating rate was about 10°C/min. Two different types of electrodes were studied. One was an unpatterned carbon film, the second sample was a patterned electrode array. The projected areas for both types of electrodes were identical. Galvanostatic and voltammetry experiments were carried out. The voltammetry experiments were carried out using a sweep rate of 0.1 mV/s over the potential range 10 mV to 2 V vs. Li/Li1.


It is very difficult to design positive tone chemistry to achieve the necessary transparency and to achieve reasonable exposure doses while maintaining excellent sidewall angles. Very thick positive Novolak photoresists also have the characteristic of forming voids after exposure as a result of the nitrogen generated during exposure. Also, positive photoresists require three coats to achieve a thickness of;65 mm. The LIGA process in which PMMA resist is exposed with an X-ray source has demonstrated structures of the order of 1 mm deep.

Despite the good adhesion of SU-8, the post patterns peeled from the substrate when using a one-step pyrolysis process at 900°C in a vacuum furnace. This problem was finally solved when switched to the two-step pyrolysis procedure. The patterned carbon electrode exhibits the general electrochemical behavior. C-MEMS electrode array is electrochemically reversible for lithium and the pyrolyzed SU-8 array characteristics are similar to coke characteristics. The results showed that the 3D C-MEMS electrode array has approximately 80% higher capacity than the 2D unpatterned carbon film. The explanation for the increased capacity is the carbon posts ‘ added effective size.

The C-MEMS array has a higher internal resistance which results in a considerable overpotential. This higher resistance stems from the fact that the posts ‘ height is almost two orders of magnitude larger than the unpatterned film’s thickness. The overpotential can be significantly reduced by applying smaller currents and the capacity increases.


We effectively accomplished high proportion carbon posts (10:1) by pyrolyzing SU-8 negative photoresist in a straightforward one-turn step process. These C-MEMS cluster anodes display reversible intercalation/deintercalation of lithium.

The higher lithium limit of the C-MEMS anode cluster proposes that C-MEMS comprises a great way to deal with building 3D carbon microelectrode exhibits for microbattery applications. Such clusters might be associated with C-MEMS leads and empower changing to high voltage or high current relying upon the current application.


  1. M. Balkanski, Sol. Energy Mater. Sol. Cells, 62, 21 (2000)
  2. K. Kinoshita, in Handbook of Battery Materials, J. O. Besenhard, Editor, p. 231, Wiley- VCH, Weinheim (1999).
  3. R. W. Hart, H. S. White, B. Dunn, and D. R. Rolison, Electrochem. Commun., 5, 120 (2003).
  4. J. W. Long, B. Dunn, D. R. Rolison, and H. S. White, Chem. Rev. ~Washington, D.C  

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