  We report on a quantum dot device design that combines the low disorder
properties of undoped SiGe heterostructure materials with an overlapping gate
stack in which each electrostatic gate has a dominant and unique function --
control of individual quantum dot occupancies and of lateral tunneling into and
between dots. Control of the tunneling rate between a dot and an electron bath
is demonstrated over more than nine orders of magnitude and independently
confirmed by direct measurement within the bandwidth of our amplifiers. The
inter-dot tunnel coupling at the (0,2)<-->(1,1) charge configuration
anti-crossing is directly measured to quantify the control of a single
inter-dot tunnel barrier gate. A simple exponential dependence is sufficient to
describe each of these tunneling processes as a function of the controlling
gate voltage.
