Miller, 27, has been at the Riverside Stadium since last January but failed to hold down a regular first-team spot and made just 12 appearances.
He joined Boro from the Scottish Premier League side Aberdeen, and previously played for Dundee United and Bristol City.
"I have not had a lot of chances in the Championship to be honest with Middlesbrough so hopefully fingers crossed I can work my way into this team and make a contribution," he told the Iron's official website.
"It's been very frustrating at Middlesbrough, I felt I did well in training and when I played in the reserves but I just didn't get given the chance that I wanted. "I just want to play games and score the goals that keep us up.
Goalkeeper Joe Murphy looks likely to miss out again with the ankle problem that ruled him out of last weekend's goalless home draw with Burnley.
Cliff Byrne and Rob Jones are bidding to shake off injuries and could come into contention and centre-back David Mirfin has been passed fit for action.
Fefender Niall Canavan, midfielder Michael O`Connor and winger Garry Thompson remain long-term absentees.