Action Details
Requirements and how-to articles for Google Ads's action:

paid action
This ad format expands to 970 x 415 while politely "pushing" all page elements downwards. The first user impression delivers an auto-initiated push-down experience. All subsequent impressions deliver a user-initiated push-down which expands via a user click. This size is ideal to showcase High-Definition content such as videos, photos, animations and applications. Suitable for text ads and display ads.

Requirements
You need this to get it done:

Large Leaderboard
You can create a responsive display ad, or upload a display ad. You can also choose to copy existing ads.
You can upload image ads as .gif, .jpg and .png
You can upload AMPHTML ads as a .zip containing 1 HTML document and up to 39 media assets.
Maximum file size: 150KB
Dimensions: 970 x 90 pixels (expands to 970 x 415 pixels)
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

0
Google AdSense Help - Guide to Ad Sizes
List of different ad sizes and how well each one performs.
Official
Link missing here or found errors? Improve How-Tos