the dielectric liner 112 for example wet etching may be done using tetramethylammonium hydroxide tmah or potassium hydroxide koh to remove a portion of the substrate 106 and leave the dielectric liner 112 intact alternatively dry etching based on hydrogen bromide hbr chemistry can be used which has good selectivity to the dielectric liner 112 continuing now with reference to fig3 a portion of the dielectric liner 112 has been etched away from the tip of the electrodes 102 exposing the electrodes 102 as illustrated in fig4 a dielectric layer 120 may optionally be used to insulate the remaining heavily doped region 110 of the substrate in exemplary embodiments the dielectric layer 120 may a polymer such as polymethylmethacrilate pmma a spin on glass or another suitable alternative turning now to fig5 another exemplary embodiment of a high density multi electrode array 500 is illustrated the high density multi electrode array 500 includes a silicon on insulator soi wafer that is used in the transistor layer 508 above a buried oxide layer box 514 in one exemplary embodiment as illustrated in fig6 a during the fabrication of the high density multi electrode array 500 a portion of the heavily doped region 510 of the substrate can be etched to a desired depth alternatively as shown in fig6.