essentially no thermal quasiparticles in the devices. At these temperatures and in a device in which there is no trapped magnetic flux, Q$_{i}$ should be dominated by losses in the microstrip dielectric. This expression for the responsivity of a microstrip MKID can be combined with the known amplifier noise, providing a closed form expression that can predict the sensitivity of the MKID at a given readout power level. Previous work with lumped element resonators [15] has shown that hydrogen rich amor- phous silicon (a-Si:H) is a promising material, with a low power loss tangent tan( δ ) ∼ 2 × 10 − $^{5}$. A low loss tangent, and hence a higher internal quality factor since tan( δ ) = 1 /Q$_{i}$ , is vital for microstrip MKIDs. A higher Q$_{i}$ will directly lead to resonators with higher sensitivity when using a readout scheme based on dissipation. A readout based on dissipation, and not phase, will likely be required since the two-level system (TLS) contribution to the noise equivalent power (NEP) in the phase direction from the deposited dielectric is expected to be much higher than the NEP in the dissipation direction [16, 17]. In this work microstrip resonators with aluminum wiring and an a-Si:H dielectric have been fabricated. The geometry is illustrated in Figure 1. The resonators were fabricated with optical lithography and dry etching techniques. First, a 93 nm thick aluminum film is deposited to form a CPW feed line and a ground plane with small ground plane holes to suppress effects from stray magnetic fields. This layer is then patterned with a dry etch in an inductively coupled plasma (ICP) etcher. A 200 nm thick film of a-Si:H is then deposited at a temperature of 100 C to form the insulating dielectric layer. To make a quarter wave device, a via could now be etched in the a-Si:H using the ICP to form a short to the bottom wiring layer, while a half wave resonator will have an open end without a via. A 154 nm thick layer of aluminum is then sputtered. This layer is patterned by an ICP to form the top conductor of the microstrip. This forms microstrip resonators with a width w of 4 µ m and lengths between 3.9 and 6.0 mm. The strength of the coupling ( Q$_{c}$ ) of the microstrip to the feedline is determined by the amount of microstrip line that covers the CPW feedline. Finally, the a-Si:H insulating layer is patterned with the ICP to allow easy wire bonding, and the silicon wafer is diced into 7.5 × 2 mm chips. The chips are glued into a gold-plated copper sample box with GE varnish and wire bonded to transition boards which convert from the coaxial input lines to a CPW transmis- sion line. The box is placed inside an adiabatic demagnetization refrigerator (ADR) capable 4