\section{Introduction}
\label{sec:introduction}

In this paper, we present results from a test sensor
which was designed to investigate a novel approach
to electromagnetic calorimeters (ECAL).
In this approach, the
readout of the ECAL is binary, meaning that each channel
returns a yes/no result with no further amplitude 
information. The motivation for such a calorimeter is
presented in~\cite{ref:introduction:decal}. 

Although the potential applications for a binary ECAL are
wide, the sensor discussed in this paper was designed to study
a specific application, namely the International Linear
Collider (ILC)~\cite{ref:introduction:ilc}. 
The work presented in this paper
has been done within the context of the
CALICE Collaboration~\cite{ref:introduction:calice},
which is studying calorimetry for future linear colliders.

In the rest of this paper,
the design and fabrication of the test sensor are 
presented in section~\ref{sec:design}.
Section~\ref{sec:simulation} describes the simulations
used for modelling the sensor response.
Sections~\ref{sec:testp} and \ref{sec:pixel} presents
results of individual pixel measurements, from test pixels
with analogue readout and bulk pixels with digital readout,
respectively.
Finally, section~\ref{sec:sensor} describes
results of sensor-wide measurements.
