Thermoformed electrode arrays

1. A cochlear lead comprising:

a thermoformed circuit comprising:

a substrate;

electrodes formed on the substrate, wherein the electrodes are shaped to curve around a longitudinal axis of the cochlear lead;

traces formed on the substrate and connected to the electrodes; and

intermediate sections between the electrodes, wherein, when the lead is straight prior to implantation in a cochlea, at least a portion of the intermediate sections are curved around an axis that is orthogonal to the longitudinal axis.

2. The cochlear lead of claim 1 , wherein the thermoformed circuit further comprises a basal extension formed into a tube, an interior of the tube forming a lumen to receive a stylet.

3. The cochlear lead of claim 1 , wherein proximal intermediate sections curve around the longitudinal axis and distal intermediate sections curve around the axis that is orthogonal to the longitudinal axis.

4. The cochlear lead of claim 1 , wherein the electrodes comprise a curled left edge and a curled right edge, wherein the curled left edge and the curled right edge curl into an interior of the cochlear lead and are surrounded by a flexible encapsulant.

5. The cochlear lead of claim 1 , wherein the electrodes comprise a three dimensional surface with a compound curvature about two different axes.

6. The cochlear lead of claim 1 , further comprising cutouts between the electrodes to increase flexibility of the cochlear lead, wherein the cutouts are larger between distal electrodes and smaller between proximal electrodes to make a distal portion of the cochlear lead more flexible than a proximal portion of the cochlear lead and wherein the cutouts on a first side of the cochlear lead are larger than the cutouts on a second side of the cochlear lead to make the cochlear lead bend into an ascending spiral.

7. The cochlear lead of claim 6 , further comprising flexible silicone that fills cutouts between electrodes.

8. The cochlear lead of claim 7 , wherein the flexible silicone filling the cutouts is in tension when the cochlear lead is straight.

9. The cochlear lead of claim 1 , further comprising tabs extending from the electrodes, in which the tabs are joined to form rings around a central lumen of the cochlear lead.

10. The cochlear lead of claim 1 , wherein the substrate comprises:

a flexible substrate in which the electrodes are formed on a first surface of the flexible substrate and traces are formed on a second surface of the flexible substrate; and

a thermoplastic layer adhered to the thermoformed circuit to cover the traces.

11. A method comprising:

patterning traces and electrodes on a substrate;

bonding the substrate to a thermoplastic layer;

thermoforming the substrate and thermoplastic layer into a predetermined shape to form a thermoformed circuit, wherein the predetermined shape comprises electrodes curved around a first longitudinal axis and intermediate portions joining the electrodes, the intermediate portions curved about a second axis that is orthogonal to the longitudinal axis when the circuit is straightened along the longitudinal axis; and

liquid injection molding silicone around the thermoformed circuit.

12. The method of claim 11 , further comprising removing silicone flash from the electrodes using a laser operation, wherein the laser operation also forms a predetermined surface texture on the electrodes.

13. The method of claim 11 , wherein thermoforming comprises:

aligning the circuit and thermoplastic layer by passing an alignment feature in a thermoforming mold through an aperture in a flag extension formed in the thermoplastic layer; and

pressing the substrate and thermoplastic layer into a mold cavity.

14. The method of claim 11 , wherein thermoforming comprises joining a first edge of the thermoplastic layer to a second edge of the thermoplastic layer to form a continuous tube.

15. The method of claim 11 , wherein thermoforming comprising joining a first tab extending from a first side of an electrode with a second tab extending from a second side of the electrode.