Readout Characteristic of Integrated Monolithic InGaAs Active Pixel Sensor Array

A newly fabricated Mcaolithic InGaAs Active Pixel Image Sensor’z is presented, and its readout characteristics are described. The sensor is fabricated fhrn InCfiAs epitaxirdly deposited on an InP substrate. It consists of an InGaAs photodiode connected to InP depletion-mode Junction field effect transistors (J-s) for signal buffering, selection and reset. The monolithic sensor eliminates the need for hybridization with a silicon multiplexer, and in addition, atlows the sensor to b front ilhm~inate4 making it sensitive to visible as well as IR radiation. Wltb further development, the sensor is ideaI for dual band (Visible41R) applications, includktg optical communication. It is also well suited to applications requiring near room temperature, broad band response such as for atmospheric gas sensing and target identification. ‘Iwo different types of small 4x 1 test arrays have been fabricated. One is a source follower pa detector architecture. IIere the signal charge is integrated on the photodiodc capacitance. The photodiodc is connected to a gate of a JI I1;l” configured as a source-follower, which buffers the photodiode voltage. Ihe other test circuit uses a capacitive trartsimpedance amplifier. This circuit contains an inverl= using an input JIET with a passive JFET load. The pbotodiode is connected to the JFET gate. A feed back capacitor causes the circuit to act as an integrator, while keqing the diode input bMs relatively ConSkWt. Both circuits atso contain JI1;T switches for reset and selection. Selection connects the output of the chosen cell onto a common output bus. lhe other test circuit uses a source follower per detector architecture. }Iere the signal charge is integrated on the photodiode capacitance. lle photodiode is connected to a gate of a JfT:T configured as a source-follower, which buffers the photodiode voltage, Both circuits also contain Jl~lT switches for reset and selection. Selection connects the output of the chosen cell onto a common output bus. In this exploratory development effort, the effectiveness of these two different readout circuits will be discussed in terms of leakage, operating frequency, and temperakrrc. lhese results then will guide for the second pbasc demonstration of integrated two dimensional monolithic active pixel sensor arrays for application in transportable shiptxwd surveillance, night vision and emission spectroscopy.