Zynga, the popular gaming company behind hits such as Farmville — and the owner of other smash titles such as Words with Friends on Android and iPhone — has filed for an initial public offering (IPO), The New York Times reported on Friday. It currently has a $20 billion valuation and has plans to offer 10% of its shares; Morgan Stanley will work on the deal. Mark Pincus, the company’s CEO, expects that Zynga can earn $1 billion through the IPO. Unlike some other recent tech IPOs, which have caused many to claim the industry is in the midst of a “tech bubble,” Zynga has had solid earnings through its business model, which typically relies on in-app purchases for in-game currency. The firm reportedly recorded a profit of $90.6 million in 2011 on revenues of nearly $600 million. Zynga currently remains the top-dog when it comes to gaming on Facebook — it has 272.5 million active users across its biggest titles such as Cityville and Farmville.