I'm not sure if you have a syntax error in your
LinkButton
or was it just a problem with posting the snippet, nevertheless you can try this:
<asp:LinkButton runat="server" ID="lbtnHome" Text="Home" OnClientClick="window.document.forms[0].target='_blank';" />
Or use this:
<asp:HyperLink ID="hlHome" runat="server" NavigateUrl='~' Target="_blank">Home</asp:HyperLink>