In our analysis of Spitzer /IRS archival data on the stellar and sub-stellar members of the TW Hydrae Association ( TWA ) , we have discovered two new brown dwarf disks : a flat optically thick disk around SSSPM J1102-3431 ( SSSPM 1102 ) , and a transition disk around 2MASS J1139511-315921 ( 2M1139 ) .
The disk structure for SSSPM 1102 is found to be very similar to the known brown dwarf disk 2MASSW J1207334-393254 ( 2M1207 ) , with excess emission observed at wavelengths as short as 5 \micron .
2M1139 shows no excess emission shortward of \sim 20 \micron , but flares up at longer wavelengths , and is the first transition disk detected among the sub-stellar members of TWA .
We also report on the Spitzer /70 \micron observations , and the presence of an absorption 10 \micron silicate feature for 2M1207 .
The absorption can be attributed to a close to edge-on disk at a 75 \arcdeg inclination .
The 10 \micron spectrum for 2M1207 shows crystalline forsterite features , with a peak in absorption near 11.3 \micron .
No silicate absorption/emission is observed towards SSSPM 1102 .
While only 6 out of 25 stellar members show excess emission at these mid-infrared wavelengths , all of the TWA brown dwarfs that have been observed so far with Spitzer show signs of disks around them , resulting in a disk fraction of at least 60 % .
This is a considerable fraction at a relatively older age of \sim 10 Myr .
A comparison with younger clusters indicates that by the age of the TWA ( \sim 10 Myr ) , the disk fraction for brown dwarfs has not decreased , whereas it drops by a factor of \sim 2 for the higher mass stars .
This suggests longer disk decay time scales for brown dwarfs compared to higher mass stars .