On-chip inductor using redistribution layer and dual-layer passiviation

Abstract

A system and method utilize a redistribution layer in a flip-chip or wirebond package, which is also used to route signals to bumps, as a layer for the construction of an on-chip inductor or a layer of a multiple-layer on-chip inductor. In one example, the redistribution layer is surrounded by dual-layer passivation to protect it, and the inductor formed thereby, from the environment and isolate it, and the inductor formed thereby, from the metal layer beneath it.

What is claimed is: 
     
         1 . A method, comprising:
 forming a metal layer;   forming a first passivation layer over the metal layer;   forming a via through the first passivation layer to the metal layer;   forming a redistribution layer on the first passivation layer and through the via in the first passivation layer, such that the redistribution layer contacts the first metal layer;   forming a second passivation layer over the redistribution layer; and   forming an inductor at least partially in the redistribution layer.   
     
     
         2 . The method of  claim 1 , wherein a thickness of the redistribution layer is based on a desired Q factor. 
     
     
         3 . The method of  claim 2 , wherein the redistribution layer is the furthest metal layer from a substrate layer. 
     
     
         4 . The method of  claim 1 , further comprising:
 forming a second metal layer;   forming a dielectric layer between the metal layer and the second metal layer, the dielectric layer having a channel therethrough; and   forming a connection device between the first metal layer and the second metal layer and through the channel in the dielectric layer.   
     
     
         5 . The method of  claim 4 , wherein:
 the inductor comprises a multiple-layer passive electrical element, and forming the multiple-layer passive electrical element comprises:
 forming a first layer in the redistribution layer; 
 forming a second layer in the metal layer; and 
 forming a third layer in the second metal layer. 
   
     
     
         6 . The method of  claim 1 , wherein forming the inductor further comprises:
 forming a first layer of the inductor in the redistribution layer; and   forming a second layer of the inductor in the metal layer.   
     
     
         7 . The method of  claim 1 , further comprising:
 forming a second inductor in the metal layer, such that the inductor in the redistribution layer and the second inductor in the metal layer form a transformer.   
     
     
         8 . The method of  claim 1 , further comprising:
 forming a second inductor in the redistribution layer, such that the inductor and the second inductor in the redistribution layer form a transformer.   
     
     
         9 . The method of  claim 1 , wherein the first and second passivation layers comprise a same material. 
     
     
         10 . The method of  claim 1  wherein the first and second passivation layers comprise different materials. 
     
     
         11 . The method of  claim 1 , wherein the redistribution layer comprises a low resistivity metal. 
     
     
         12 . The method of  claim 1 , wherein the redistribution layer comprises aluminum or copper. 
     
     
         13 . The method of  claim 1 , wherein the first and second passivation layers comprise nitride. 
     
     
         14 . The method of  claim 1 , wherein one of the first and second passivation layers comprises a nitride and another one of the first and second passivation layers comprises a polyimide. 
     
     
         15 . The method of  claim 1 , wherein the redistribution layer is encapsulated between the first and second passivation layers. 
     
     
         16 . An apparatus, comprising:
 a metal layer;   a first passivation layer formed on the metal layer, the first passivation layer having a channel therethrough running to the metal layer;   a redistribution layer formed on the first passivation layer and formed in the channel, such that the redistribution layer contacts the metal layer and is configured to route signals;   a second passivation layer formed on the first passivation layer and the redistribution layer; and   a passive electrical element at least partially formed in the redistribution layer, the passive electrical element including a transformer comprising first and second inductors,   wherein the first inductor is formed in the redistribution layer and the second inductor is formed in the metal layer.   
     
     
         17 . The apparatus of  claim 16 , further comprising:
 a substrate layer,   wherein the redistribution layer is the furthest metal layer from the substrate layer, and   wherein a thickness of the redistribution layer is based on a desired Q factor of the passive electrical element.   
     
     
         18 . The apparatus of  claim 16 , wherein:
 the passive electrical element comprises a multiple-layer passive electrical element;   a first layer is formed in the redistribution layer; and   a second layer is formed in the metal layer.   
     
     
         19 . The apparatus of  claim 17 , further comprising:
 a second metal layer;   a dielectric layer formed between the first metal layer and the second metal layer, the dielectric layer having a channel therethrough; and   a connection device formed between the first metal layer and the second metal layer and through the channel in the dielectric layer.   
     
     
         20 . The apparatus of  claim 17 , wherein the first and second passivation layers comprise different materials.