We report the fabrication process and performance characterization of a fully integrated ferroelectric gate stack in a WSe2/SnSe2 Tunnel FETs (TFETs). The energy behavior of the gate stack during charging and discharging, together with the energy loss of a switching cycle and gate energy efficiency factor are experimentally extracted over a broad range of temperatures, from cryogenic temperature (77 K) up to 100 degrees C. The obtained results confirm that the linear polarizability is maintained over all the investigated range of temperature, being inversely proportional to the temperature T of the ferroelectric stack. We show that a lower-hysteresis behavior is a sine-qua-non condition for an improved energy efficiency, suggesting the high interest in a true NC operation regime. A pulsed measurement technique shows the possibility to achieve a hysteresis-free negative capacitance (NC) effect on ferroelectric 2D/2D TFETs. This enables sub-15 mV dec(-1) point subthreshold slope, 20 mV dec(-1) average swing over two decades of current, I-ON of the order of 100 nA mu m(-2) and I-ON/I-OFF > 10(4) at V-d = 1 V. Moreover, an average swing smaller than 10 mV dec(-1) over 1.5 decades of current is also obtained in a NC TFET with a hysteresis of 1 V. An analog current efficiency factor, up to 50 and 100 V-1, is achieved in hysteresis-free NC-TFETs. The reported results highlight that operating a ferroelectric gate stack steep slope switch in the NC may allow combined switching energy efficiency and low energy loss, in the hysteresis-free regime.